Base station apparatus, wireless communication system, and wireless transmission method

ABSTRACT

Allocation of transmission power is carried out adaptively without affecting adjacent cells. Included are a reception part that receives information from a mobile station apparatus, a transmission power determination part that determines transmission power when transmitting a wireless signal to a mobile station apparatus based on the received information, an acquisition part that acquires information about communication environment in each time channel or each frequency channel from the received information, a scheduling part that identified a time channel or frequency channel the relationship of which between transmission power and communication environment satisfies the condition for allocation and allocates transmission data and transmission power for transmission to a mobile station apparatus to a communication slot in the time channel or frequency channel, and a transmission part that transmits a wireless signal using the communication slot to which the transmission data and the determined transmission power have been allocated.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of application Ser. No. 11/665,569filed on Apr. 17, 2007 now abandoned, which is a National Phase of PCTInternational Application No. PCT/JP2005/019195 filed on Oct. 19, 2005.The entire contents of all of the above applications is herebyincorporated by reference.

TECHNICAL FIELD

The present invention relates to a base station apparatus, a wirelesscommunication system, and a wireless transmission method, which carryout the allocation of transmission power adaptively without affectingadjacent cells.

BACKGROUND ART

In our country, the service of IMT-2000 (International MobileTelecommunication 2000) was started in October 2001 before the rest ofthe world, and thus the transmission and access technique in a mobilecommunication system is rapidly developing. In addition, the techniqueof HSDPA (High Speed Down-link Packet Access) and the like arestandardized and the data transmission at about 10 Mbps at maximum isnow being put to practical use.

On the other hand, the standardization to realize a broad band wirelessInternet access that targets a transmission rate of 10 Mbps to 100 Mbpsis in progress and various techniques have been proposed. The conditionrequired to realize high transmission rate wireless communication is theimprovement of frequency usage efficiency. Since the transmission rateand the used bandwidth are in a proportional relationship, a simplesolution to increase the transmission rate is to widen the frequencybandwidth to be used. However, available frequency bands are in a tightsituation and it is unlikely that a sufficient bandwidth is allocatedwhen constructing a new wireless communication system. Consequently, itbecomes necessary to improve the frequency usage efficiency.

In addition, another required condition is to provide service in aprivate area (isolated cell), such as a wireless LAN, in a seamlessmanner while realizing service in a communication area constituted bycells, such as a mobile phone.

Techniques having the possibility of solving these problems include atechnique called one-cell reuse OFDM/(TDMA, FDMA) (Orthogonal FrequencyDivision Multiplexing/Time Division Multiple Access, Frequency DivisionMultiple Access). This is a technique in which communication isperformed using the same frequency in all of the cells in acommunication area constituted by cells, the modulation scheme whenperforming communication is the OFDM, and the access scheme uses theTDMA and FDMA. This is a communication system, without doubt, capable ofrealizing higher-speed data communication in an isolated cell whilemaintaining a common wireless interface with a cell area.

The OFDM, TDMA, and FDMA, which are constitutional techniques of theOFDM/(TDMA, FDMA), are explained briefly.

First, the OFDM is a technique used for IEEE802.11a, which is a wirelesssystem of 5 GHz band, and a terrestrial digital broadcasting. The OFDMis a system in which tens to thousands of carriers are arranged atintervals of a minimum frequency that does not cause interferencetheoretically and communication is performed simultaneously. In thenormal OFDM, such a carrier is called a sub-carrier and each sub-carrieris modulated when performing communication by a modulation scheme, suchas the PSK, QAM, etc. Further, with an error correction techniquecombined, it has grate resistance to frequency selective fading. In thepresent specification, the number of sub-carriers used in the OFDM isassumed to be 768.

Next, the TDMA is an access system in which time is divided whentransmitting/receiving data. Normally, in a communication system usingthe TDMA as an access system, a frame configuration is used in whichthere are a plurality of slots, which is a unit of communication time,and further, it is general to allocate a control slot necessary forreceiving a frame at the front of the frame in the case of Down-link. Inthe present specification, it is assumed that a frame is composed ofnine slots and the front slot is allocated as a control slot.

Next, the FDMA is an access system in which frequencies are divided whentransmitting/receiving data. Normally, in a communication system usingthe FDMA as an access system, frequencies are divided into severalbands, which are frequency bands for performing communication, and thusterminals (mobile station apparatus) that access are classified.Normally, a protective band called a guard band is prepared betweendivided frequency bands, however, in the OFDM/(TDMA, FDMA), no guardband is used because the frequency usage efficiency is decreased, or ifused, its band is very narrow, just for accepting several sub-carries.In the present specification, 768 sub-carries used in the OFDM aredivided into 12 groups, each group including 64 sub-carries, forperforming the FDMA.

Next, the OFDM/(TDMA, FDMA) is explained based on the above-describedintroduction. FIG. 42 is a diagram showing a two-dimensional frameconfiguration of the OFDM/(TDMA, FDMA). In FIG. 42, the vertical axisrepresents the frequency and the horizontal axis represents the time.One of a plurality of rectangles shown in FIG. 42 is the minimum unitused for data transmission, composed of a plurality of OFDM symbols, andis referred to as a slot in the present specification. Among the slots,those with diagonals are control slots. In this case, the figure meansthat there are nine slots in the time direction and 12 slots in thefrequency direction in one frame, that is, there exist a total of 108slots (among then, 12 slots are control slots) in one frame. Inaddition, in the present specification, a group of slots in thedirection of the frequency axis at the same time (composed of 12 slotsin the case of FIG. 42) is referred to as a time channel and a group ofslots in the direction of the time axis at the same frequency (composedof nine slots in the case of FIG. 42) is referred to as a frequencychannel. In form, a slot is denoted by (Tn, Fm), a time channel isdenoted by Tn (n is a natural number from 1 to 9), and a frequencychannel is denoted by Fm (m is a natural number from 1 to 12). Forexample, the hatched slot in FIG. 42 is a slot denoted by (T4, F7).

Next, communication from a base station (referred to as AP or basestation apparatus) to a mobile station (referred to as MT, mobilestation apparatus, or simply “terminal”) is considered. When an APallocates data of 15 slots to an MT, it is assumed that the data isallocated to the slots with vertical lines in FIG. 42, although theremay be various cases. In other words, the data to be received by the MTis allocated to (T2 to T4, F1), (T5 to T8, F4), and (T2 to T9, F11).Further, in order to indicate that the AP has allocated data to the MT,it is necessary to embed data indicative of the allocation to thecontrol slot of the frequency to be used. In the case of this example,(T1, F1), (T1, F4), and (T1, F11) correspond to the control slots.

The OFDM/(TDMA, FDMA) system is a system in which a plurality of mobilestations transmit and receive data to and from the base station bychanging the frequency and time based on those described above. In FIG.42, the figure is drawn such that there seems to be a gap between slotsfor convenience's sake, however, the presence or absence of a gap is ofno importance.

FIG. 43 is a block diagram showing a general configuration of atransmission circuit used in the OFDM/(TDMA, FDMA). The transmissioncircuit shown in FIG. 43 has a data multiplex part 431. In addition, thetransmission circuit has 12 error correction encoding parts 432-a to432-1 and at the same time, has 12 serial/parallel conversion parts (S/Pconversion parts) 433-a to 433-1. A transmission power control part 435exhibits a function of changing transmission power for each frequencychannel.

In the data multiplex part 431, information data is separated into 12groups in units of packets for transmission. In other words, the datamultiplex part 431 physically specifies the ODFM/(TDMA, FDMA) slot to bespecified by a module, such as a CPU etc., not shown schematically here.After that, error correction encoding is performed in the errorcorrection encoding parts 432-a to 432-1, separation into 64 groups isperformed in the S/P conversion parts 433-a to 433-1, and each carrieris modulated in a mapping part 434. In the transmission power controlpart 435, power control is performed into transmission power for eachsub-channel specified by a module, such as a CPU etc., not shownschematically and IFFT (Inverse Fast Fourier Transform) processing isperformed in an IFFT part 436. When generating an OFDM signal of 768waves, the number of points of the IFFT normally used is 1,024.

After that, in a P/S conversion part 437, conversion into serial data isperformed and then a guard interval is inserted in a guard intervalinsertion part 438. A guard interval is inserted in order to reduceinterference between symbols when receiving an OFDM signal. Then, afterconverted into an analog signal in a D/A conversion part 439 andconverted into a frequency for transmission in a radio transmission part440, the data is transmitted from an antenna part 441.

In addition, FIG. 44 is a block diagram showing a general configurationof a reception circuit used in the OFDM/(TDMA, FDMA). The receptioncircuit shown in FIG. 44 has a data demultiplex part 461 and further,has 12 error correction decoding parts 460-a to 460-1. In addition, thereception circuit has 12 parallel/serial conversion parts (P/Sconversion parts) 459-a to 459-1.

In the reception circuit, an operation reverse to that of thetransmission circuit is performed basically. The frequency of the radiowave received by an antenna part 451 is converted into a frequency in afrequency band in which A/D conversion is possible by a radio receptionpart 452. With data having been converted into a digital signal in anA/D conversion part 453, the OFDM symbols are synchronized in asynchronization part 454 and the guard interval is removed in a guardinterval removal part 455. After that, the data is paralleled into 1,024data in an S/P conversion part 456.

After that, the FFT of 1,024 points is performed in an FFT (Fast FourierTransform) part 457 and demodulation of the sub-carrier of 768 waves isperformed in a propagation channel estimation and demapping part 458.Normally, propagation path is estimated by the receiver by sending aknown signal from the transmitter to the receiver. After that, thenecessary data is serialized in the P/S conversion parts 459-a to 459-1,error correction is performed in the error correction decoding parts460-a to 460-1, and the data is input to the data demultiplex part 461.In the data demultiplex part 461, the data is processed into informationdata and output.

Next, the outline of a communication system consisting of cells isexplained. FIG. 45( a) is an example of the case where cells have ahexagonal shape and seven frequency bands are used. A base station isarranged in the center of the cell and in cell B0, communication isperformed using a frequency band Fc0, in B1, Fc1 is used, and similarcombinations follow in the rest of the cells. In such a cellconfiguration in which the number of frequency bands is sufficient, itis unlikely that the adjacent cells use the same frequency and it ispossible to perform communication in an excellent condition withoutinfluence from the adjacent cells.

FIG. 45( b) is an example of the case where one-cell reuse OFDM/(TDMA,FDMA) is used. Similarly, the configuration consists of hexagonal cells,however, the same frequency Fc0 is used. Consequently, when the one-cellreuse OFDM/(TDMA, FDMA) operates ideally, it follows that a frequencyusage efficiency seven times that compared to the case in FIG. 45( a)can be attained. As a result, it can be said that realization ofone-cell reuse is a indispensable technique in order to realize highspeed communication.

As obvious also from FIG. 45( b), the point that affects the idealoperation of the one-cell reuse is to prevent interference from othercells. Two techniques can roughly be thought as a method for preventinginterference from other cells. One method is to establish acommunication system in which each terminal removes radio waves fromother cells (interference removal) and the other method is to preventinterference from affecting as much as possible. Among these methods,the following two are explained with respect to a specific technique ofthe latter method.

First, a wireless data communication system, a wireless datacommunication method, and its program disclosed in Japanese UnexaminedPatent Publication No. 2003-18091 (Patent document 1) are explained. Acell configuration relating to the invention described in Patentdocument 1 is shown in FIG. 46. In FIG. 46, a hexagon constructed by thedotted-line is shown in each cell in comparison with FIG. 45( a). Thismeans that one cell is divided into two areas, one being near the basestation and the other, distant therefrom. When cell B0 is focused on,communication is performed conventionally using a frequency Fc0 withterminals in the area distant from the base station and communication isperformed using Fc1 to Fc6 with terminals in the area near the basestation. It is described that this increases the frequency usageefficiency. Further, it is explained that the use of a sector antennawithin an area surrounded by the dotted-line increases the efficiency.This is a technique that utilizes the fact that even the use of thefrequency bands Fc1 to Fc6 does not affect the adjacent cells because itis possible to lower transmission power when performing communicationwith terminals near the base station.

Next, a mobile communication system, a base station apparatus, and acontrol method of a mobile communication system disclosed in JapaneseUnexamined Patent Publication No. 2003-46437 (Patent document 2) areexplained. A cell configuration relating to the invention disclosed inPatent document 2 is shown in FIG. 47. In FIG. 47, two hexagonsconstructed by the dotted-line are shown in each cell in comparison withFIG. 45( a). When cell B0 is focused on, the area most distant from thebase station is denoted by Ts1, the second most distant area is denotedby Ts2, and the nearest area is denoted by Ts3. Ts represents time andTs1 to Ts3 constitute one frame. This means that in B0, transmissionpower is increased to the maximum during Ts1 and communication isperformed, and then, the transmission power is lowered in Ts2 and Ts3and communication is performed. Similarly, each cell performscommunication by changing transmission power in accordance with thetime, respectively.

In B0, when communication is being performed with increased transmissionpower during Ts1, communication with transmission power increased to themaximum is not being performed in other adjacent cells, and therefore,it is possible to perform communication in B0 in a state in whichinterference from other cells is small. For the cells B1 to B6, the sameadvantage is secured similarly.

Patent document 1: Japanese Unexamined Patent Publication No. 2003-18091

Patent document 2: Japanese Unexamined Patent Publication No. 2003-46437

DISCLOSURE OF THE INVENTION

However, even if the techniques described in Patent document 1 andPatent document 2 are used in the one-cell reuse OFDM/(TDMA, FDMA), itis not possible to deal adaptively with the case of an isolated cell orthe case where the number of adjacent cells is different, and further,the case where a base station is newly installed after the base stationhas once been installed and the service has been started. Further, inPatent document 2, that each base station is synchronized with anotheris a tacit assumption and there is no description on the solving meanswhen not synchronized.

The present invention has been developed the above-describedcircumstances being taken into account and an object thereof is toprovide a base station apparatus, a wireless communication system, and awireless communication method capable of carrying out the allocation oftransmission power adaptively without affecting adjacent cells.

(1) In order to attain the above-mentioned object, the present inventionhas employed means as follows. In other words, a base station apparatusaccording to the present invention is a base station apparatus that usesa plurality of slots and performs wireless communication with a mobilestation apparatus in a cell, characterized in that the base stationapparatus receives information from the mobile station apparatus,determines transmission power to be allocated to a group of the slots aswell as determining transmission power when transmitting a wirelesssignal to the mobile station apparatus based on the receivedinformation, determines a group of slots or part of a group of slots fortransmitting transmission data based on the transmission power whentransmitting the wireless signal to the mobile station apparatus and thetransmission power allocated to the group of slots, and transmits thewireless signal to the mobile station apparatus using the determinedgroup of slots or the determined part of the group of slots.

As described above, since the base station apparatus determines thetransmission power to be allocated to the group of the slots as well asdetermining the transmission power when transmitting the wireless signalto the mobile station apparatus based on the received information anddetermines the group of slots or the part of the group of slots fortransmitting the transmission data based on the transmission power whentransmitting the wireless signal to the mobile station apparatus and thetransmission power allocated to the group of slots, it is possible tocarry out the allocation of transmission power adaptively withoutaffecting the adjacent cells.

(2) In addition, a base station apparatus according to the presentinvention is a base station apparatus that has a plurality of timechannels and performs wireless communication with a mobile stationapparatus in a cell using the time channel, characterized in that thebase station apparatus receives information from the mobile stationapparatus, determines transmission power to be allocated to the timechannel as well as determining transmission power when transmitting awireless signal to the mobile station apparatus based on the receivedinformation, determines a time channel or part of time channel fortransmitting transmission data based on the transmission power whentransmitting the wireless signal to the mobile station apparatus and thetransmission power allocated to the time channel, and transmits thewireless signal to the mobile station apparatus using the determinedtime channel or the determined part of time channel.

As described above, since the base station apparatus determines thetransmission power to be allocated to the time channel as well asdetermining the transmission power when transmitting the wireless signalto the mobile station apparatus based on the received information anddetermines the time channel or the part of time channel for transmittingtransmission data based on the transmission power when transmitting thewireless signal to the mobile station apparatus and the transmissionpower allocated to the time channel, for example, small transmissionpower is allocated to a time channel with large interference power, atime channel with small SINR, and a time channel with a large error ratebecause those time channels are used only on the central part of thecell as those not used on the peripheral part of the cell because oftheir large interference. In addition, large transmission power isallocated to a time channel with small interference power, a timechannel with large SINR, and a time channel with a small error rate asthose used on the peripheral part of the cell because their interferenceis small even on the peripheral part of the cell. Due to this, it ismade possible to carry out the allocation of transmission poweradaptively without affecting the adjacent cells.

(3) In addition, a base station apparatus according to the presentinvention is a base station apparatus that has a plurality of frequencychannels and performs wireless communication with a mobile stationapparatus in a cell using the frequency channel, characterized in thatthe base station apparatus receives information from the mobile stationapparatus, determines transmission power to be allocated to thefrequency channel as well as determining transmission power whentransmitting a wireless signal to the mobile station apparatus based onthe received information, determines a frequency channel or part offrequency channel for transmitting transmission data based on thetransmission power when transmitting the wireless signal to the mobilestation apparatus and the transmission power allocated to the frequencychannel, and transmits the wireless signal to the mobile stationapparatus using a frequency channel corresponding to the determinedfrequency channel or the determined part of frequency channel.

As described above, since the base station apparatus determines thetransmission power to be allocated to the frequency channel as well asdetermining the transmission power when transmitting the wireless signalto the mobile station apparatus based on the received information anddetermines the frequency channel or the part of frequency channel fortransmitting transmission data based on the transmission power whentransmitting the wireless signal to the mobile station apparatus and thetransmission power allocated to the frequency channel, for example,small transmission power is allocated to a frequency channel with largeinterference power, a frequency channel with small SINR, and a frequencychannel with a large error rate because those frequency channels areused only on the central part of the cell as those not used on theperipheral part of the cell because of their large interference. Inaddition, large transmission power is allocated to a frequency channelwith small interference power, a frequency channel with large SINR, anda frequency channel with a small error rate as those used on theperipheral part of the cell because their interference is small also onthe peripheral part of the cell. Due to this, it is made possible tocarry out the allocation of transmission power adaptively withoutaffecting the adjacent cells.

(4) In addition, a base station apparatus according to the presentinvention is characterized in that the condition for determining theallocation of time channel or part of time channel, or frequency channelor part of frequency channel for transmitting the transmission data isany one of the following conditions that: the interference power at themobile station apparatus is the smallest; the magnitude of transmissionpower and the magnitude of interference power at the mobile station areassociated in advance in a relationship of inverse proportion andinterference power corresponding to the determined transmission power ispossessed; and the ratio between reception signal power and interferencepower at the mobile station apparatus is the maximum.

By determining the condition for allocation as described above, it ismade possible to carry out the allocation of transmission poweradaptively without affecting the adjacent cells.

(5) In addition, a base station apparatus according to the presentinvention is characterized in that when determining the allocation oftime channel or part of time channel, or frequency channel or part offrequency channel for transmitting the transmission data, the basestation apparatus divides the mobile station apparatus in the cells intoa plurality of groups based on the information received from the mobilestation apparatus and allocates slots for transmitting transmission datato the same time channel or the same frequency channel for a mobilestation apparatus in the same group.

As described above, by grouping the mobile station apparatus in thecell, the allocation of transmission power can be carried out for eachgroup, and therefore, it is made possible to perform the allocationprocessing efficiently. In addition, it is possible to efficiently carryout the allocation of transmission data and transmission power for amobile station apparatus that newly makes a request for connection inthe same cell. Due to this, it is made possible to carry out theallocation of transmission power adaptively without affecting theadjacent cells. By the way, the transmission power of each group mayassume discrete values or may assume continuous values in theabove-mentioned numerical value range.

(6) In addition, a base station apparatus according to the presentinvention is characterized in that when determining the allocation oftime channel or part of time channel, or frequency channel or part offrequency channel for transmitting the transmission data, the basestation apparatus identifies the group to which the transmission powerfor transmitting a wireless signal to any one of the mobile stationapparatus in the cell belongs, and allocates, when there exists a vacanttime channel or a vacant frequency channel in all of the individual timechannels or the individual frequency channels or in the part thereof towhich transmission power corresponding to a group with transmissionpower larger than that of the identified group has been allocated, aslot for transmitting transmission data to the mobile station apparatusto the vacant time channel or the vacant frequency channel.

With this configuration, it is possible to employ a form in which, whenthere exists a vacant channel in the time channels or the frequencychannels that have been allocated to a group that requires hightransmission power, the allocation of a terminal that requires lowtransmission power to the vacant slot of the time channels or thefrequency channels allocated to a terminal group that requires hightransmission power is allowed. This is because the possibility is highthat the time channel or the frequency channel to which a terminal groupthat requires high transmission power has been allocated is allocated aterminal group that requires low transmission power in the adjacentcells and there will occur no interference between the adjacent cellseven when a terminal that requires low transmission power is allocatedto the vacant communication slot of the time channel or the frequencychannel in question. Due to this, it is made possible to carry out theallocation of transmission power adaptively without affecting theadjacent cells.

(7) In addition, a base station apparatus according to the presentinvention is characterized in that when determining the allocation oftime channel or part of time channel, or frequency channel or part offrequency channel for transmitting the transmission data, the basestation apparatus identifies the group to which the transmission powerfor transmitting a wireless signal to any one of the mobile stationapparatus in the cell belongs, and allocates, when transmission data isnot allocated to the time channel or the frequency channel allocated tothe identified group and when there exists a vacant time channel or avacant frequency channel in all of the time channels or the frequencychannels or in the part thereof to which transmission powercorresponding to a group with transmission power smaller than that ofthe identified group has been allocated, a slot for transmittingtransmission data to the mobile station apparatus to the vacant timechannel or the vacant frequency channel.

As described above, since when allocating the transmission power to thespecific mobile station apparatus, the base station apparatus allocates,when there exists a vacant communication slot in the time channels oreach of the frequency channels to which transmission power correspondingto the group with transmission power smaller than the group to which thetransmission power for the mobile station apparatus belongs has beenallocated, the transmission data to be transmitted to the mobile stationapparatus and the transmission power corresponding to the group withsmall transmission power to the vacant communication slot, it is madepossible to carry out the allocation of transmission power adaptivelywithout affecting the adjacent cells.

(8) In addition, a base station apparatus according to the presentinvention is characterized by changing, after allocating a slot fortransmitting the transmission data, the transmission power of theallocated slot based on the received information.

As described above, since the base station apparatus changes, afterallocating the slot for transmitting the transmission data, thetransmission power of the allocated slot based on the receivedinformation, it is made possible to use a plurality of values asreception power on the mobile station apparatus side in accordance withthe variation in the propagation path.

(9) In addition, a base station apparatus according to the presentinvention is characterized by changing the modulation scheme whenallocating transmission data to be transmitted to the mobile stationapparatus and the transmission power to the vacant time channel or eachvacant frequency channel.

As described above, since the base station apparatus changes themodulation scheme when allocating the transmission data to betransmitted to the mobile station apparatus and the transmission powerto the vacant communication slot, it is possible to avoid the influenceon the adjacent cells while avoiding the occurrence of an error bychanging the modulation scheme to a lower one, that is, to a modulationscheme for easier reception, as well as lowering the transmission powerwhen, for example, transmitting a wireless signal to a mobile stationapparatus that requires high transmission power, and if thecommunication slot of each time channel or each frequency channel towhich low transmission power has been allocated is vacant. On thecontrary, it is possible to avoid the influence on the adjacent cellswhile improving transmission efficiency by changing the modulationscheme to a higher one as well as raising transmission power when, forexample, transmitting a wireless signal to a mobile station apparatusthat requires low transmission power, and if the communication slot ofeach time channel or each frequency channel to which high transmissionpower has been allocated is vacant

(10) In addition, a base station apparatus according to the presentinvention is characterized by updating the allocated transmission powerat intervals of a certain period of time when determining the allocationof time channel or part of time channel, or frequency channel or part offrequency channel for transmitting the transmission data.

As described above, since the base station apparatus updates theallocated transmission power at intervals of a certain period of time,it is made possible to allocate transmission power in accordance withthe movement of the mobile station apparatus, the change in thesituation of propagation path, etc.

(11) In addition, a base station apparatus according to the presentinvention is characterized by updating the allocated transmission powerwhen determining the allocation of time channel or part of time channel,or frequency channel or part of frequency channel for transmitting thetransmission data, and if there exists a mobile station apparatus thatnewly makes a request for connection in the cell and if any one of themobile station apparatus moves, or if the situation of propagation pathchanges in any one of the mobile station apparatus.

With this configuration, it is made possible to allocate transmissionpower in accordance with the variation in the situation of communicationin the cell in real time.

(12) In addition, a base station apparatus according to the presentinvention is characterized by allocating transmission power so that,when updating the transmission power, the difference between thetransmission power immediately before the update and the transmissionpower to be allocated at the time of update is equal to or less than afixed value.

As described above, since the base station apparatus allocates thetransmission power so that the difference between the transmission powerimmediately before the update and the transmission power to be allocatedat the time of update is equal to or less than a fixed value, it is madepossible to keep the variation in interference with the adjacent cellsto a minimum. Here, the difference shall be equal to or less than afixed value because of an attempt to define a range in which thetransmission power immediately before update does not changeconsiderably after the update. A specific numerical value range can befound from the technical common sense in the communication technique.

(13) In addition, a base station apparatus according to the presentinvention is characterized by allocating, when determining theallocation of time channel or part of time channel, or frequency channelor part of frequency channel for transmitting the transmission data,transmission power with which a wireless signal can reach the entirerange in the cell to at least one of the time channels or frequencychannels and at the same time, transmission power the influence of whichon the adjacent cells can be ignored to at least one of the timechannels or frequency channels.

By thus allocating transmission power, it is made possible to dealflexibly even with the case where there appears a mobile stationapparatus that newly makes a request for connection in the cell and themobile station apparatus requires high transmission power or lowtransmission power.

(14) In addition, a base station apparatus according to the presentinvention is characterized by acquiring a level of interference receivedfrom the adjacent cells based on information received from the mobilestation apparatus and determining the time channel or part thereof, orthe frequency channel or part thereof to which the transmission powerwith which the wireless signal can reach the entire range in the cell isallocated in accordance with the measured interference level in order totransmit data other than the control data.

As described above, since the base station apparatus determines the timechannel or part thereof, or the frequency channel or part thereof towhich the transmission power with which the wireless signal can reachthe entire range in the cell is allocated in accordance with themeasured interference level, it is possible to evaluate only the timechannel or the part thereof, or the frequency channel or the partthereof that is actually affected by the interference from the adjacentcells and it is made possible to improve the usage efficiency of thetime channel or the part thereof, or the frequency channel or the partthereof.

(15) In addition, a base station apparatus according to the presentinvention is characterized by measuring the number of adjacent cellsbased on the information received from the mobile station apparatus anddetermining, when determining the allocation of time channel, frequencychannel, or communication slot for transmitting the transmission data, anumber L of the time channels or part thereof, or the frequency channelsor part thereof to which the transmission power with which the wirelesssignal can reach the entire range in the cell is allocated in accordancewith the measured interference level in order to transmit data otherthan the control data as such one that holds.L≦(total number of time channels, frequency channels, or communicationslots)/{(number of adjacent cells)+1}.

As described above, since the base station apparatus dynamically changesthe number of time channels or the part thereof, or the number offrequency channels or the part thereof to which the transmission powerwith which the wireless signal can reach the entire range in the cell isallocated in accordance with the number of adjacent cells, it is madepossible to improve the usage efficiency of the time channel or the partthereof, or the frequency channel or the part thereof.

(16) In addition, a base station apparatus according to the presentinvention is characterized by allocating, when determining theallocation of time channel or part of time channel, or frequency channelor part of frequency channel for transmitting the transmission data andif on one hand, there exists a mobile station apparatus required totransmit a wireless signal with transmission power with which thewireless signal can reach the entire range in the cell and if, on theother hand, there exists no data to be transmitted to the mobile stationapparatus, dummy data to be transmitted to the mobile station apparatusand the transmission power with which the wireless signal can reach theentire range in the cell to the time channel or the part thereof, or thefrequency channel or the part thereof.

With such a configuration, it is made easy to detect a channel with highinterference power at each terminal of the adjacent cells.

(17) In addition, a base station apparatus according to the presentinvention is characterized by adding a hysteresis characteristic to thecondition for the change of groups when the group to which thetransmission power allocated to the mobile station apparatus belongs ischanged due to the information received from the mobile stationapparatus.

With such a configuration, it is made possible to perform the groupingoperation stably without being affected considerably from situations inwhich the communication speed is not constant and the communicationspeed needs to be changed frequently at the mobile station apparatus.

(18) In addition, a wireless communication system according to thepresent invention is characterized by being configured by the basestation apparatus according to any one of claim 1 to claim 17 and atleast one mobile station apparatus.

According to the wireless communication system according to the presentinvention, it is made possible to carry out the allocation oftransmission power adaptively without affecting the adjacent cells.

(19) In addition, a mobile station apparatus according to the presentinvention is characterized by being applied to the wirelesscommunication system according to claim 18.

According to the mobile station apparatus according to the presentinvention, it is made possible to carry out the allocation oftransmission power adaptively without affecting the adjacent cells.

(20) In addition, a wireless communication method according to thepresent invention is a wireless communication method of a base stationapparatus having a plurality of time channels and transmitting awireless signal to a mobile station apparatus using the time channel,characterized by comprising at least a step for receiving informationfrom the mobile station apparatus, a step for determining transmissionpower when transmitting a wireless signal to the mobile stationapparatus based on the received information, a step for acquiringinformation about communication environment in each time channel fromthe received information, a step for determining the allocation of timechannel or part of time channel and transmission power for transmissionto the mobile station apparatus based on the determined transmissionpower and the information about communication environment, and a stepfor transmitting a wireless signal to the mobile station apparatus usingthe time channel or the part of time channel to which the transmissiondata and the determined transmission power have been allocated.

As described above, since the transmission power when transmitting thewireless signal to the mobile station apparatus is determined and at thesame time, the transmission power to be allocated to the time channel isdetermined based on the information received from the mobile stationapparatus, and the time channel or part of time channel for transmittingtransmission data is determined based on the transmission power whentransmitting the wireless signal to the mobile station apparatus and thetransmission power allocated to the time channel, for example, smalltransmission power is allocated to a time channel with largeinterference power, a time channel with small SINR, and a time channelwith a large error rate because those time channels are used only on thecentral part of the cell as those not used on the peripheral part of thecell because of their large interference. In addition, largetransmission power is allocated to a time channel with smallinterference power, a time channel with large SINR, and a time channelwith a small error rate as those used on the peripheral part of the cellbecause their interference is small also on the peripheral part of thecell. Due to this, it is made possible to carry out the allocation oftransmission power adaptively without affecting adjacent cells.

(21) In addition, a wireless communication method according to thepresent invention is a wireless communication method of a base stationapparatus having a plurality of frequency channels and transmitting awireless signal to a mobile station apparatus in a cell using thefrequency channel, characterized by comprising at least a step forreceiving information from the mobile station apparatus, a step fordetermining transmission power when transmitting a wireless signal tothe mobile station apparatus based on the received information, a stepfor acquiring information about communication environment in eachfrequency channel from the received information, a step for determiningthe allocation of frequency channel or part of frequency channel andtransmission power for transmitting transmission data to the mobilestation apparatus based on the determined transmission power and theinformation about communication environment, and a step for transmittinga wireless signal to the mobile station apparatus using the frequencychannel or the part of time channel to which the transmission data andthe determined transmission power have been allocated.

As described above, since the transmission power when transmitting thewireless signal to the mobile station apparatus is determined and at thesame time, the transmission power to be allocated to the frequencychannel is determined based on the information received from the mobilestation apparatus, and a frequency channel or part of frequency channelfor transmitting transmission data is determined based on thetransmission power when transmitting the wireless signal to the mobilestation apparatus and the transmission power allocated to the frequencychannel, for example, small transmission power is allocated to afrequency channel with large interference power, a frequency channelwith small SINR, and a frequency channel with a large error rate becausethose frequency channels are used only on the central part of the cellas those not used on the peripheral part of the cell because of theirlarge interference. In addition, large transmission power is allocatedto a frequency channel with small interference power, a frequencychannel with large SINR, and a frequency channel with a small error rateas those used on the peripheral part of the cell because theirinterference is small also on the peripheral part of the cell. Due tothis, it is made possible to carry out the allocation of transmissionpower adaptively without affecting adjacent cells.

According to the present invention, since transmission power whentransmitting a wireless signal to a mobile station apparatus isdetermined and at the same time, transmission power to be allocated to agroup of slots is determined based on information received from themobile station apparatus, and a group of slots or part of a group ofslots for transmitting transmission data is determined based on thetransmission power when transmitting the wireless signal to the mobilestation apparatus and the transmission power allocated to the group ofslots, it is possible to carry out the allocation of transmission poweradaptively without affecting adjacent cells.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1( a) is a diagram showing an arrangement situation of a cell andmobile station terminals, FIG. 1( b) is a diagram showing transmissionpower required for Down-link in the cell, and FIG. 1( c) is a diagramshowing an example of the allocation of slots.

FIG. 2 is a diagram showing a configuration example of slots.

FIG. 3 is a diagram showing an example of cell arrangement.

FIG. 4 is a diagram showing transmission timing of a control slot group.

FIG. 5 is a block diagram showing a general configuration of a mobilestation apparatus.

FIG. 6 is a block diagram showing a general configuration of a basestation apparatus.

FIG. 7 is a flow chart showing the operation of the allocation of slotat a base station apparatus.

FIG. 8 is a flow chart showing the operation of the allocation of slotat a mobile station apparatus.

FIG. 9( a) is a diagram showing an arrangement situation of mobilestation apparatus in cell 1 and cell 2, FIG. 9( b) is a diagram showingtransmission power required for Down-link in the cell 2, and FIG. 9( c)is a diagram showing a situation of the allocation of slot in the cell2.

FIG. 10( a) is a diagram showing transmission power required forDown-link in the cell 1 and FIG. 10( b) shows a diagram showingtransmission power required for Down-link in the cell 2.

FIG. 11 is a diagram showing a situation of the allocation of mobilestation apparatus in the cell 2 and interference power affecting thecell 1.

FIG. 12 is a diagram showing a state in which slots have been allocatedto mobile station apparatus A to C in the cell 1.

FIG. 13 is a diagram showing transmission power required for Down-linkin the cell 1 and the cell 2 and a state in which slots have beenallocated to mobile station apparatus D to H in the cell 1.

FIG. 14 is a diagram showing how the transmission power level and theinterference level are associated with each other.

FIG. 15( a) is a diagram showing the case where the transmission timingof the control slot group is fixed and FIG. 15( b) is a diagram showingthe case where the transmission timing of the control slot group isvariable.

FIG. 16 is a diagram showing an example in which the transmission powerrequired for Down-link and the allocation of slot in the same group arechanged.

FIG. 17 is a diagram showing the transmission power required forDown-link and an example in which the allocation to the time channel towhich another group has been allocated is allowed.

FIG. 18 is a diagram showing a general configuration of a mobile stationapparatus.

FIG. 19 is a diagram showing a general configuration of a base stationapparatus.

FIG. 20 is a diagram showing an example of a sub-channel used inDown-link.

FIG. 21 is diagram showing a configuration example of a frame.

FIG. 22( a) is a diagram showing the configuration of a slot and FIG.22( b) is a diagram showing the outline of the topology of a network.

FIG. 23( a) is a diagram showing the outline of a cell arrangement andFIG. 23( b) is a diagram showing a structure example of a control slot.

FIG. 24 is a diagram showing the relationship between the cell boundaryand the transmission power group.

FIG. 25 is a flow chart showing the outline of the operation procedureof a mobile station apparatus.

FIG. 26 is a flow chart showing the outline of the operation procedureof a base station apparatus.

FIG. 27 is a flow chart showing the operation of the allocation ofsub-channel that can be used.

FIG. 28 is a flow chart showing a connection process.

FIG. 29 is a flow chart of transmission power control.

FIG. 30 is a flow chart showing the determination of the allocation ofsub-channel.

FIG. 31 is a flow chart showing the operation of the allocation oftransmission data to slots.

FIG. 32 is a flow chart showing the operation of the allocation oftransmission data to slots.

FIG. 33 is a diagram showing the relationship between the cell boundaryand the transmission power group.

FIG. 34 is a diagram showing the relationship between the cell boundaryand the transmission power group.

FIG. 35 is a diagram showing the relationship between the cell boundaryand the transmission power group.

FIG. 36 is a diagram showing the relationship between the cell boundaryand the transmission power group.

FIG. 37 is a diagram showing the relationship between the cell boundaryand the transmission power group.

FIG. 38 is a diagram showing the relationship between the cell boundaryand the transmission power group.

FIG. 39 is a diagram showing the relationship between the cell boundaryand the transmission power group.

FIG. 40 is a flow chart showing the operation of the allocation ofsub-channel that can be used.

FIG. 41 is a flow chart showing the operation of the allocation ofsub-channel that can be used.

FIG. 42 is a diagram showing a configuration example of a frame.

FIG. 43 is a diagram showing a general configuration of a base stationapparatus.

FIG. 44 is a diagram showing a general configuration of a mobile stationapparatus.

FIG. 45( a) is a diagram showing an example of a cell arrangement andFIG. 45( b) is a diagram showing an example of a cell arrangement.

FIG. 46 is a diagram showing an example of a cell arrangement.

FIG. 47 is a diagram showing an example of a cell arrangement.

FIG. 48 is a diagram showing how to give hysteresis to grouping.

FIG. 49 is a diagram showing an example of a condition in grouping.

FIG. 50 is a flow chart showing the operation of a base station.

FIG. 51 is a flow chart showing the operation of a terminal.

BEST MODES FOR CARRYING OUT THE INVENTION First Embodiment

A method of allocation of slot according to a first embodiment of thepresent invention is explained below. In the method of allocation ofslot according to the first embodiment of the present invention, aplurality of terminals that require a transmission power level of thesame level in a base station are allocated adaptively to differentfrequency channels of the same time channel while taking intoconsideration the influence of interference that comes from adjacentcells. An example of the result of the allocation when such adaptiveallocation of slot is carried out is shown in FIG. 1. By the way, it isassumed that the “base station” has the same meaning as the controlstation, AP, or base station apparatus and the “mobile station” has thesame meaning as the MT, mobile station apparatus, or terminal.

FIG. 1( a) shows a cell and the arrangement of terminals in the cell andFIG. 1( b) shows transmission power required for the Down-linkcommunication for the respective terminals in the cell. However, in thefirst embodiment of the present invention, it is assumed that thetransmission of transmission power control is so performed that thereception power of all of the terminals in the cell is the same. In sucha situation, when the method of allocation of slot according to thefirst embodiment of the present invention is applied, the terminalswhose transmission power required for the Down-link is the same levelare grouped. Here, grouping is such that terminal A, terminal B, andterminal C are put into group 1, terminal D, terminal E, terminal F, andterminal G are put into group 2, and terminal H and terminal I are putinto group 3. Then, it follows that the terminals belonging to the samegroup are allocated to different frequency channels of the same timechannel. Here, it is assumed that the group 1 is allocated to timechannel 3, the group 2, to time channel 2, and the group 3, to timechannel 5. As a result, such channel allocation as shown in FIG. 1( c)is carried out and the transmission power required for the Down-linkcommunication to a terminal is maintained at the same level for eachtime channel and therefore it is possible to keep the averageinterference power affecting on adjacent cells substantially constantfor each time channel. A channel allocation procedure by such adaptiveallocation of slot is explained below.

First, a slot configuration according to the first embodiment of thepresent invention is shown in FIG. 2. As shown in FIG. 2, the slotconfiguration according to the first embodiment of the present inventionis assumed to be a configuration in which the number of frequencychannels is 12, the number of time channels including control slots(hereinafter, a single time channel for transmission of controlinformation in a single frequency channel is referred to as a controlslot and the time channels for transmission of control information overa plurality of frequency channels are referred to as a control slotgroup) is 9, and the same frequency band is used in all of the cells. Inthe following, explanation is given with an example of a system in whichbase stations are synchronized with each other, however, the presentinvention is not limited to a system in which base stations aresynchronized with each other but can also be applied to a system inwhich base stations are not synchronized with each other as in the caseof the synchronized system.

In addition, in the case of the system in which base stations aresynchronized with each other, it may also be possible to assume that thecell arrangement is a state as shown in FIG. 3 and that the transmissiontiming of the control slot group is one common to all of the cells asshown in FIG. 4( a), and further that the configuration is such one inwhich timing is different for each cell as shown in FIG. 4( b).Furthermore, it may also be possible to assume a configuration in whichthe transmission timing of the control slot is different from frequencychannel to frequency channel. A case where the control slot group istransmitted with common timing determined in advance in all of the cellsis explained below.

First, a device configuration of terminals when the allocation of slotaccording to the first embodiment of the present invention is carriedout is shown in FIG. 5. FIG. 5 is a block diagram of a deviceconfiguration of terminals. In FIG. 5, reference number 100 denotes anantenna part, 101 denotes a radio reception part, 102 and 111 denote anA/D conversion part, 103 denotes a symbol synchronization part, 104denotes a guard interval removal part, 105 denotes an S/P part, 106denotes an FET part, 107 denotes a propagation channel estimation anddemapping part, 108 denotes a P/S part, 109 denotes an error correctiondecoding part, 110 denotes a demultiplex part, 112 denotes an RSS(Received Signal Strength) measurement part, 113 denotes an interferencepower measurement part, 114 denotes a control part, and 115 denotes anUp-link transmission part.

As shown in FIG. 5, a terminal that is carrying out the allocation ofslot according to the first embodiment of the present invention has theRSS measurement part 112, unlike the conventional example, and performsmeasurement of a reception power level at Down-link. In addition,measurement of interference power is performed at the interference powermeasurement part 113. However, in FIG. 5, the interference powermeasurement part is at the post stage of the FFT part 106 and has aconfiguration in which the transmission power of an interference signalafter FFT is measured, but, not limited to this, and a configuration maybe possible in which the transmission power of an interference signalbefore FFT is measured.

The RSSI (Received Signal Strength Indicator) thus measured issubtracted from the transmission power information of a base stationincluded in the control information transmitted from the base station atthe control part 114 and thereby a propagation loss is calculated. Theinformation about the propagation loss and the interference power ineach time channel is put together with other information data as apacket at the control part 114 and transmitted to the base station atthe Up-link transmission part 15.

Processes other than the above (demodulation of information data etc.)are performed in the same manner as that of the prior art. First, thereceived signal is subjected to symbol-synchronization at thesynchronization part 113 via the A/D conversion part 102. After that,the guard interval is removed at the guard interval (GI) removal part104 and after subjected to serial/parallel conversion at the S/Pconversion part 105, the received signal is transmitted to the FFT part106 and converted from a signal in the time area into a signal in thefrequency area. For the received signal thus converted into one in thefrequency area, propagation channel estimation and demapping areperformed at the propagation channel estimation and demapping part 107,and after the parallel/serial conversion at the P/S conversion part 108,the transmission data is decoded at the error correction decoding part109 and transmitted to the demultiplex part, as a result.

FIG. 6 is a block diagram of a device configuration of a base station.In FIG. 6, reference number 120 denotes a scheduling part, 121 denotes amultiplex part, 122 denotes an error correction encoding part, 123denotes an S/P part, 124 denotes a mapping part, 125 denotes atransmission power control part, 126 denotes an IFFT part, 127 denotes aP/S part, 128 denotes a guard interval insertion part, 129 denotes a D/Aconversion part, 130 denotes a radio transmission part, 131 denotes anantenna part, and 132 denotes an Up-link reception part.

As shown in FIG. 6, a base station when the allocation of slot accordingto the first embodiment of the present invention is carried outtransmits the propagation loss information and interference informationobtained from the Up-link reception part to the scheduling part 120unlike the conventional example, and carries out the allocation of slotaccording to the first embodiment of the present invention. Then, at aslot allocated by the scheduling part 120, transmission of informationdata of each terminal is performed as a result, and at the same time,the transmission power control information for each terminal is obtainedfrom the scheduling part 120 and transmitted to the transmission powercontrol part 125.

Next, a flow chart of allocation of slot at a base station according tothe first embodiment of the present invention is shown in FIG. 7 andFIG. 8. A control flow shown in FIG. 7 and FIG. 8 is explained below, inwhich each terminal in cell 1 in FIG. 9( a) is actually put into a groupand channel allocation is carried out. Here, it is assumed that in cell2 (adjacent cell of the cell 1) in FIG. 9( a), the allocation of channeland slot has already been carried out and the situation of the channelallocation is such one as shown in FIG. 9( c). At this time, it is alsoassumed that each of terminals Ito T in the cell 2 is at each ofpositions shown in FIG. 9( a), respectively, and the transmission power(transmission power required for Down-link) in the base stationcorresponding to the respective terminals is such one as shown in FIG.9( b).

In the situation as described above, when there occurs a request forcommunication in the terminal A, terminal B, and terminal C situated inthe cell 1, first, as shown in FIG. 7 and FIG. 8, the terminals A to Creceive (step S21) the control information of all of the frequencychannels transmitted (step S2) periodically in the control slot groupfrom the base station in each cell, and measures the RSSI of thereceived signal at each terminal as shown in step S22. It is assumedthat the control slot group transmitted periodically from the basestation in each cell is transmitted with transmission power that can bereceived by even a terminal situated at the edge of the cell and thecontents of the control information include transmission powerinformation (information indicative of the magnitude of transmissionpower used for the transmission) when the base station transmits controlinformation, information about allocation of slot, etc.

After the measurement of the RSSI at each terminal, the terminals A to Cdemodulate the received signal, as shown in step S23 and obtain thetransmission power information at the base station when the controlinformation is transmitted. Next, from the transmission powerinformation at the base station obtained in step S24 and the RSSIobtained in step S22, the amount of attenuation of radio waves on thepropagation path (propagation loss: here it is assumed that propagationloss=transmission power−RSSI) is calculated (step S25).

Further, as shown in step S26, measurement of the interference powerthat comes from the adjacent cells is performed at each of the terminals(terminals A to C). The terminals A to C notify the base station of theinterference power thus obtained and the propagation loss information ofDown-link between the base station and the terminal obtained in step S26via the Up-link (step S27).

By the procedure described above, it is possible for the base station toobtain the propagation loss information of the Down-link between thebase station and the terminal and the information about interferencepower that comes from the adjacent cells necessary to carry out theadaptive allocation of slot according to the first embodiment of thepresent invention for each terminal.

Next, at the base station, as shown in step S5 to step S7 in FIG. 7, theterminals are grouped based on the propagation loss information at eachterminal obtained via the Up-link. Here, the grouping of terminals is aprocess, as shown in FIG. 10( a), in which the transmission powerrequired for performing Down-link transmission for each terminal iscalculated from the propagation loss at each terminal (step S6) and theterminals having the same transmission power as a result of thecalculation are handled as a group (step S7).

By the way, as shown in FIG. 9( b), FIG. 10( a), and FIG. 10( b),explanation is given on the assumption that the transmission power ofthe Down-link for each terminal assumes discrete values, however, notlimited to this example, the present invention can also be applied tothe case where the transmission power of the Down-link for each terminalassumes continuous values.

As shown in FIG. 10( a), here, the transmission power of the Down-linkfor the terminal A is the same level as that of the transmission powerof the Down-link for the terminal C, and as a result, they belong to thesame group (here, the group 2). In addition, the terminal B requireshigh transmission power and therefore it belongs to a group (here, thegroup 1) different from that of the terminals A and C.

As described above, after the terminals (here, the terminals A to C)having a request for communication are put into a group, the allocationof time channel to each group and the allocation of frequency channel toeach terminal belonging to the group are carried out at the basestation. By the method of allocation of slot according to the firstembodiment of the present invention, the allocation of time channel iscarried out in the order from the group with higher transmission powerof the Down-link (step S8). Consequently, here, the allocation of timechannel is carried out from the group 1 (to which only the terminal Bbelongs) and as shown in step S9, whether there exists a terminal towhich a slot has already been allocated in the selected group (group 1)is determined. Here, only the terminal B that newly initiatescommunication belongs to the group 1, and therefore, the procedure movesto step S10 and the time channel with the lowest interference powerobserved at the terminal B of the group 1 among the vacant time channels(here, all of the time channels) is allocated to the group 1.

As shown in FIG. 11, the interference power in the time channel 4 is theminimum among the interference power of each time channel observed inthe cell 1 and the time channel 4 is allocated to the group 1. As shownin FIG. 11, the interference power affecting the cell 1 is the minimumin the time channel 4, and this is because the terminals I to K situatednear the base station of the cell 2 and whose transmission power of theDown-link is set low are allocated to the time channel 4.

By such a procedure, the allocation of time channel to the group 1 iscarried out and next, the allocation of frequency channel to eachterminal belonging to the relevant group is carried out (step S11 tostep S13). First, as shown in step S11, the amount of data of Down-linkfor the terminal (terminal B) to which a slot has not been allocated yetin the relevant group (here, the group 1) is calculated, and as shown instep S12, the number of frequency channels necessary for one frame iscalculated. Then, as shown in step S13, the allocation of vacantfrequency channel to the relevant terminal in accordance with the numberof necessary frequency channels. Here, if the number of necessaryfrequency channels of the terminal B is assumed to be three, it followsthat three frequency channels of the time channel 4 are allocated to theterminal B, as shown in FIG. 12.

As above, the allocation of slot to the group 1 is completed, however,since there remain other groups to which allocation must be carried outin addition to the group 1, the procedure returns to step 8 and theallocation of time channel to the relevant group (here, the group 2) iscarried out. If the allocation of time channel to the group 2 is carriedout in the same manner as the above, the time channel 7 whoseinterference power is the smallest of all but the time channel alreadyallocated to the group 1 is allocated to the group 2, as a result.

After the allocation of time channel for each group, in the same manneras in the above, the allocation of frequency channel to the terminals Ato C belonging to the group 2 to which the time channel has beenallocated is carried out and thus the procedure of the allocation ofslot is completed. The result of such allocation of slot is notified tothe terminal in the cell by the control slot group (step S16, step S17)and after that, each terminal occupies the allocated slot for a fixedperiod of time and performs communication.

Here, when the allocation of slot in the first embodiment of the presentinvention is updated and the allocation to a certain time channel ischanged to a terminal group different from the previous frame, it isdesirable to operate the algorithm so as to allocate, if possible, aterminal group that requires transmission power close to that of theterminal group to which the relevant time channel has been allocated inthe previous frame in order to keep the variation in the interferencewith the adjacent cells to a minimum.

The result of the allocation of slot so far is shown in FIG. 12. Asshown in FIG. 12, the terminal B that requires high transmission powerat the Down-link in the cell 1 is allocated to the same time channel asthat of the terminals I to K at which the Down-link transmission isperformed with the lowest transmission power in the cell 2. In addition,the terminals A and C having somewhat higher transmission power in thecell 1 are allocated to the same time channel as that of the terminal Lat which the Down-link transmission is performed with low transmissionpower in the cell 2.

As described above, by carrying out the allocation of slot according tothe first embodiment of the present invention, a situation in which theterminals that require high transmission power both in the adjacentcells are allocated to the same time channel is eased and interferencebetween cells can be suppressed.

Further, as to the case where a request for communication occurs newlyat the terminals D to H in the cell 1, the process of the allocation ofslot by the same procedure is explained. First, in the same manner asbefore (step S21 to step S29), each terminal having received controlinformation from the base station notifies the base station of thepropagation loss information of the Down-link and the information aboutthe interference power via the Up-link. Here, if it is assumed that theDown-link transmission power for the terminals D to H is that shown inFIG. 10( a), respectively, the terminals D and F are added to the group2 to which the terminal A and the terminal C belong. In addition, theterminal E is added to the group 1 to which the terminal B belongs andit follows that the terminal G belongs to the group 3 and the terminalF1 belongs to the group 4, respectively (step S5 to step S7).

Next, as shown in step S8, if it is assumed that the time channel isallocated in the order from the group having higher transmission powerat the Down-link, it follows that the time channel is allocated to thegroup 1 to which the terminal E belongs. At this time, the terminal Bbelongs to the group 1 and the time channel 4 has already beenallocated. Since the number of vacant frequency channels of the timechannel 4 is greater than the number of necessary frequency channels ofthe terminal E, the number of necessary frequency channels is allocatedto the terminal E among the vacant frequency channels of the timechannel 4 as a result (step S11 to step S16).

In addition, the terminals D and F are allocated to the vacant frequencychannel of the time channel 7 to which the group 2 has been allocatedbefore, however, the number of vacant frequency channels in the timechannel 7 is only three as shown in FIG. 12. If the number of necessaryfrequency channels of the terminal D is assumed to be three, it ispossible to allocate the terminal D to the time channel 7, however, ifthe number of necessary frequency channels of the terminal F is assumedto be five, it is not possible to allocate the terminal F to the timechannel 7. In such a case, the terminal D is allocated to the remainingfrequency channels of the time channel 7 and the terminal F is allocatedto the time channel to which another group is not allocated. In thismanner, control is so executed that the number of time channels to beallocated to the same group increases (steps S14 and 15).

As a result, in the time channels (the time channels 1 to 3, 5, 6, and8) to which no group is allocated, the time channel 3 having the lowestinterference power notified from the terminal F is allocated to theterminal F (group 2) and the frequency channels corresponding to thenumber of necessary frequency channels (five frequency channels) of theterminal Fare allocated.

In addition, the time channel 8 having the lowest interference powernotified from the terminal G among the remaining time channels isallocated to the group 3 to which the terminal G belongs and thefrequency channels corresponding to the number of necessary frequencychannels of the terminal G are allocated. Similarly, the time channel 6is allocated to the group 4 to which the terminal H belongs and thefrequency channels corresponding to the number of necessary frequencychannels of the terminal H are allocated.

The result of the allocation of slot described above is shown in FIG.13. As shown in FIG. 13, the terminals B and E that require hightransmission power for the Down-link in the cell 1 are allocated to thesame time channel as that of the terminals Ito K in which Down-linktransmission is performed with low transmission power in the cell 2. Inaddition, the terminals A, C, D, and F that require slightly highertransmission power for the Down link in the cell 1 are allocated to thesame time channel as that of the terminals L to O in which Down-linktransmission is performed with low transmission power in the cell 2.

Further, the terminal G and the terminal H that do not require hightransmission power in the cell 1 are allocated to the same time channelas that of the terminal T and the terminal S that require hightransmission power in the cell 2. As described above, a situation inwhich the terminals having high transmission power in the adjacent cellsare allocate to the same time channel can be eased and also in asituation in which two or more adjacent cells exist, the same allocationis carried out by repeating the above-mentioned procedure.

As described above, by repeating the procedure of the allocation of slotaccording to the first embodiment of the present invention, it ispossible to group the terminals that require transmission power of thesame level for Down-link and allocate a different time channel for eachgroup, taking into consideration the interference that comes from theadjacent cells. As described above, by allocating the slot adaptively inaccordance with the required transmission power and the interferencethat comes from the adjacent cells, a situation in which terminalshaving high transmission power both in the adjacent cells are allocatedto the same time channel is eased and by executing the same control forthe terminal that newly starts communication, it is made possible tosuppress the average interference power affecting the adjacent cellsfrom varying much, and therefore, the interference between cells can bereduced.

By setting in advance a time channel that can be used for each cell, orby setting in advance the transmission power of each time channel to adifferent value for each cell, separately from the procedure of theallocation of slot according to the present invention, it is madepossible to reduce the interference between adjacent cells, however, bysuch a method in which the time channels that can be used are limited inadvance, when there are many terminals that require the sametransmission power level in the cell, a situation will arise in whichthe allocation of time channel is not carried out despite that there arevacant time channels and therefore efficiency decreases.

In contrast to this, in accordance with the allocation of slot accordingto the present invention, the time channels that can be used are notlimited in advance and the allocation of time channel is carried outdynamically in accordance with the required transmission power and theinterference power that comes from the adjacent cells, and therefore, itis possible to flexibly deal with an increase or decrease in the numberof terminals and the addition of cells by such a control executedautonomously and dispersedly by the base station in each cell andthereby communication of high efficiency can be realized while reducingthe interference between cells.

Next, a modification example of the first embodiment of the presentinvention is shown. First, a form in which adaptive modulation isapplied is shown. In the procedure of the allocation of slot accordingto the first embodiment of the present invention, although themodulation scheme etc. of signals when user data is transmitted is notreferred to, when multi-carrier transmission such as OFDM etc. is used,it may also be possible to employ the same modulation scheme in all ofthe sub-carriers, or a form may be possible in which a differentmodulation scheme is employed for each sub-carrier, or a form may bepossible in which a modulation scheme different in terms of time is usedin accordance with the variation of the propagation channel instead ofusing the same modulation scheme at all times.

Similarly, also when the OFDM is not used in each frequency channel(when single carrier transmission is used for each frequency channel), aform is possible in which a modulation scheme different in terms of timein accordance with the propagation channel variation is used. In aprocedure in which the modulation scheme is changed in accordance withthe propagation channel variation as described above, it follows thatthe reception signal power and the interference power at the slotallocated to each terminal are measured and after the reception SINR(Signal to Interference plus Noise power Ratio) is calculated by findingits ratio, a modulation scheme in accordance with the reception SINR isselected. In this manner, by combining an adaptive modulation with theallocation of slot according to the first embodiment of the presentinvention, more efficient communication can be realized.

Next, another modification example relating to the procedure of theallocation of time channel is shown. In the procedure of the allocationof slot according to the first embodiment of the present invention, theallocation of time channel is carried out in the order from the terminalgroup that requires the highest transmission power among the terminalgroups having made a request for communication, however, on thecontrary, a procedure is possible in which the allocation of timechannel is carried out in the order from the terminal group capable ofcommunication with the lowest transmission power among the terminalshaving made a request of communication. In this case, it follows thatthe time channels having high interference power are allocated among theremaining time channels for which allocation has not been carried outyet in the order from the terminal group having the lowest transmissionpower in the Down-link.

In addition, in the first embodiment of the present invention, the timechannels with the minimum interference power measured at the terminal ofthe group are allocated among the remaining time channels for whichallocation has not been carried out yet in the order from the terminalgroup that requires the highest transmission power among the terminalgroups having made a request for communication. However, when thetransmission power required by the group having made a request forcommunication is not so high, the time channel with the minimuminterference power is allocated to the group as a result, and afterthat, even if a request for communication is made at a terminal situatednear the cell edge and a group that requires very high transmissionpower is formed, it is not possible to allocate the time channel withthe minimum interference power to a new group that requires hightransmission power.

In order to avoid such a situation, a procedure may be possible,separately from the first embodiment of the present invention, in which,as shown in FIG. 14, the interference level of each time channel isassociated with one of the transmission power levels in several stepsset in advance and on the supposition of a situation in which a groupthat requires a transmission power level higher (lower) than that of thegroup of its own is formed, the allocation of time channel based on theassociation between the transmission power level and the interferencepower level is carried out. In this case also, it is made possible todynamically deal with the circumstances because not only the timechannels with an interference level in accordance with the transmissionpower level shown in FIG. 14 are targeted for allocation, but also thetime channels not in accordance with the transmission power level arealso targeted for allocation in the case of the situation in which thenumber of terminals with the same transmission power level is large andthe allocation to the targeted time channels is not possible.

In addition, a procedure may be used, separately from the firstembodiment of the present invention, in which arbitrary time channelsamong the time channels with interference power equal to or less than athreshold value which satisfies a predetermined reception qualitydetermined in advance are allocated among the remaining time channelsfor which allocation has not been carried out yet in the order from theterminal group that requires the highest (lowest) transmission poweramong the terminal groups having made a request for communication.

Next, the contents of the control information in the Down-link, thecontents of the information to be reported from each terminal to thebase station via the Up-link, and another form relating to a method ofthe allocation of frequency channel are shown. In the first embodimentof the present invention, such a form is employed, in which the controlslot group in the Down link is used for transmitting the transmissionpower information of the base station when the control information istransmitted, and at the terminal, the propagation loss and theinterference power found from the RSSI are estimated and are reported tothe base station by the Up-link.

Separately from this, a form may be possible, in which the control slotgroup in the Down-link is used for transmitting the transmission powerinformation of the base station as in the first embodiment of thepresent invention, however, each terminal reports the measured RSSI andinterference power to the base station. In this case, after thepropagation loss in the propagation channel is calculated at the basestation from the difference between the transmission power at the basestation and the reported RSSI at the terminal, the transmission powerrequired for the Down-link transmission to each terminal is calculatedfrom the propagation loss as in the first embodiment of the presentinvention and grouping based on the transmission power of each terminalis performed. By using this form, it is possible to eliminate theprocedure to find the propagation loss and the operation part at theterminal.

In addition, separately from this, a form may be possible, in which thesame information as that in the first embodiment of the presentinvention is transmitted in the control slot group in the Down link,however, after measuring the RSSI and calculating the propagation loss,each terminal finds the transmission power control information andreports to the base station the transmission power control informationand interference power. Here, the transmission power control informationindicates the transmission power obtained by subtracting thetransmission power when the control slot group is transmitted from thetransmission power required for performing the Down-link transmissionfound from the propagation loss of each terminal and indicates how muchthe power should be raised or reduced from the transmission power of thecontrol slot group.

In addition, a form may be possible, in which the same information asthat in the first embodiment of the present invention is transmitted inthe control slot group of the Down-link, however, each terminal measuresand averages the reception signal power of each frequency channelinstead of the RSSI indicative of the reception power of the whole ofthe frequency channels and reports to the base station this togetherwith the interference power. In this case, after the propagation loss inthe propagation channel is calculated at the base station from thedifference between the transmission power at the base station and thereception power at each frequency channel, the transmission powerrequired for the Down-link transmission to each terminal is calculatedfrom the propagation loss, as in the first embodiment of the presentinvention, and grouping based on the transmission power of each terminalis performed.

Further, a form may be possible, in which the transmission powerinformation at the base station is transmitted in the control slot groupin the Down-link, as in the first embodiment of the present invention,however, each terminal measures the reception signal power of eachfrequency channel instead of the RSSI and reports to the base stationthis together with the interference power. In this case, the receptionsignal power of each frequency channel is averaged at each base stationand after the propagation loss in the propagation channel is calculatedat the base station from the difference between the transmission powerof the control information transmitted from the base station and theaverage of the reception power found before, the transmission powerrequired for the Down-link transmission to each terminal is calculatedfrom the propagation loss, as in the first embodiment of the presentinvention, and grouping based on the transmission power of each terminalis performed.

Alternatively, a form may also be possible, in which the frequencychannel to be allocated to the terminal is determined first at the basestation, and after the propagation loss (the propagation loss that hastaken into consideration the fading of the channel to be allocated) iscalculated from the difference between the transmission power of thecontrol information transmitted from the base station and the receptionpower of the frequency channel to be allocated to the terminal, thetransmission power required for the Down-link transmission to theterminal is calculated based on the propagation loss and grouping isperformed based on the result.

As described above, in the form in which the reception signal power ofeach frequency channel measured at the terminal is reported to the basestation via the Up-link, the amount of information in the Up-linkincreases and the efficiency of the Up-link decreases more or less.However, the base station grasps the reception signal power for eachfrequency channel at each terminal, and thereby, it is made possible tocarry out the allocation of frequency channel capable of obtaining themost excellent reception power for each terminal among the frequencychannels that produce a difference in the reception power due to theinfluence of fading when the frequency channel is allocated to theterminal of each group after the allocation of time channel to thegroup, and the efficiency in the Down-link increases.

In addition, by performing grouping that has taken fading intoconsideration, it is possible to limit the transmission power for eachgroup to a certain range also when the transmission power is socontrolled that the reception power of all of the terminals is constant,and it is made possible to reduce the amount of variation ininterference affecting the adjacent cells even in a situation in whichthe allocation to the terminal is changed.

Further, unlike the first embodiment of the present invention, a formmay be possible, in which information indicative of the transmissionpower of the control information is not included in the control slotgroup of the Down-link. In this case, it follows that the RSSI of thereceived control information or the reception signal power of eachfrequency channel is measured at the terminal and this is reported tothe base station together with the interference power via the Up-link.At this time, the reception signal power of each frequency channel ismay be averaged or a form may also be possible in which it is notaveraged and the information corresponding to the number of frequencychannels is reported. By employing such a form, it is possible toeliminate the control information in the Down-link.

When any one of the forms described above is used, the period of reportof the measurement result of the reception signal power and theinterference power at the terminal to the base station by the Up-linkmay be for each frame or may be at arbitrarily fixed intervals.

In addition, as described above, the transmission timing of the controlslot group in the Down-link may be common to all of the cells or may bedifferent from cell to cell (FIG. 4). Here, if the transmission timingof the control slot group in the Down-link is made common to all of thecells as shown in the first embodiment of the present invention, theDown-link control slot group is transmitted with the transmission powerthat can be received even by a terminal situated at the cell edge, andtherefore, there may the case where the control information of theadjacent cells interferes with each other at the terminal situated nearthe cell edge. When such a problem arises, by making the transmissiontiming of the control slot group in the Down-link differ from cell tocell, the situation can be avoided, in which the control informationtransmitted with the transmission power (the maximum transmission powerthat can be transmitted) that reaches the cell edge interferes with eachother.

Further, when the allocation of slot according to the present inventionis carried out, in the time channel to which the control information isallocated in the Down-link in the adjacent cell, high interference poweris measured, and therefore, it follows that the terminal group with lowtransmission power of the Down-link within the cell of its own isallocated dynamically to the same time channel. Due to this, it is alsomade possible to avoid the situation in which the control informationand the user data interfere with each other between cells.

As described above, by making the transmission timing of the controlslot group in the Down-link differ from cell to cell, it is possible toavoid the situation in which the control information transmitted withthe transmission power that reaches the cell edge interferes with eachother and by allocating the terminal with low transmission power to thetime channel to which the control information is transmitted in theadjacent cell, it is also possible to avoid the interference between thecontrol information and the user data, however, there may be the casewhere trouble occurs at the base station in the adjacent cell for somecause and a signal having very high transmission power is transmitted inthe adjacent cell in the time channel for transmitting the controlinformation in the Down-link. In such a case, because the controlinformation is affected by the interference having high transmissionpower, many terminals in the cell are disabled from communication. Asshown in FIG. 15, as a countermeasure to such a problem, a form (FIG.15( b)) may be employed, in which flexibility is given so that thetransmission timing is changed adaptively in accordance with theinterference of the adjacent cell, instead of a form (FIG. 15( a)) inwhich the control slot group in the Down-link is transmitted with apredetermined timing at all times.

This is a control in which that the interference power is measured atthe same time as the reception of the control information in theDown-link (it may also be possible to measure the SINR or detect acontrol information error) and when interference having transmissionpower exceeding a certain threshold value is observed (also when thecontrol information is erroneous successively etc.), the control slotgroup is moved to the time channel with the lowest interference poweramong the vacant time channels. When there is no vacant time channel,the communication with the terminal allocated to the time channel withthe lowest interference power is disconnected (aborted) and the controlslot group is moved to the vacant time channel.

By employing such a form, the communication of some terminals isdisconnected forcedly, however, in the situation in which the controlinformation cannot be received correctly due to the influence ofinterference, the communication of many terminals in the cell isdisconnected, and therefore, by employing the above-described form, itis possible to maintain the communication performed by many terminals inthe cell. At this time, a form may be possible in which notice to theeffect that the control slot group is moved is notified to the terminalin the frame immediately before the control slot group is moved, or aform may be possible in which such control is not executed but theterminal side is caused to have a mechanism to detect the control slotgroup over the entire the next frame when the control slot group cannotbe received at the terminal any longer.

Next, another form relating to the update timing of the allocation ofslot in accordance with the change in the surrounding environment isshown. In the first embodiment of the first invention, after theallocation of slot, each terminal performs communication by occupyingthe allocated slot for an arbitrarily fixed period of time and when theallocation to a certain time channel is changed to a terminal groupdifferent from the previous frame, a terminal group that requires thetransmission power close to that of the terminal group to which the timechannel has been allocated in the previous frame is allocated ifpossible.

In other words, after the terminal group is once allocated to a certaintime channel, the allocation is not changed if possible, or even whenchanged, the allocation is carried out to the terminal group thatrequires nearly the same transmission power. This is because a situationcan be thought in which when the terminal group to be allocated to thetime channel is changed frequently, the interference observed in theadjacent cell changes frequently and therefore interference betweenadjacent cells occurs and the receive performance are deteriorated.

In addition, this is because also when the allocation is changed to aterminal group that requires transmission power (in particular,transmission power extremely higher compared to the previous frame)largely different from the transmission power required to the terminalgroup having been allocated in the previous frame, the performance aredeteriorated due to the drastic change in the interference observed inthe adjacent cell. However, it can be thought that excellent performancecan be obtained by employing a form in which the allocation of slot isupdated in the following case.

In general, since the terminal moves also during communication, thedistance from the base station changes because of the movement and theremay be the case where transmission power different from that of thegroup to which the terminal has belonged up to now is required. Asdescribed above, a form may be possible, in which the allocation of slotis updated when the transmission power required for the Down-link haschanged accompanying the movement of the terminal, that is, the groupconfiguration has changed from the previous one. In addition, a form mayalso be possible, in which the slot allocation is updated when asituation has been encountered etc., in which interference having hightransmission power is observed at the terminal (or when the receptionSINR is deteriorated, or when data is erroneous successively) during thecommunication in the allocated slot.

In these cases, a review of the allocation of slot may be done for allof the terminals in all of the groups or a form may be possible, inwhich a review of the allocation of slot only to the terminalencountered with a situation in which the transmission power requiredfor the Down-link changes etc. is done. However, also when such a reviewof the allocation of slot is done, it is desirable to allocate theterminal group or the terminal that requires transmission power as closeas possible to that of the terminal group allocated in the previousframe to the relevant time channel (slot) in order to suppress a drasticchange in the interference affecting the adjacent cells.

In addition, in a situation in which the number of cells, such as anisolated cell, is small, it may also be possible to perform the updateof the allocation of slot frequently or to allocate a terminal groupwith transmission power largely different from that of the terminalgroup having been allocated in the previous frame to the relevant timechannel.

Next, another form relating to the case where a plurality of timechannels are allocated to one group to which a plurality of terminalsthat require the same transmission power in the Down-link belong isshown. In the first embodiment of the present invention, the number ofnecessary frequency channels per frame for the Down-link transmission iscalculated for each terminal in the group to which the time channel hasbeen allocated and the vacant frequency channels are allocated to theterminals in accordance with the number of necessary frequency channelsrequired of each terminal. Then, when the number of vacant frequencychannels of the time channel is less than the number of necessaryfrequency channels, allocation is carried out to another time channeland allocation is carried out so that a plurality of terminals thatrequire the same transmission power are accommodated in one time channelif possible.

Separately from such a form, another form may be possible, in which themaximum number of time channels that can be allocated to the terminalgroup that requires transmission power of certain level in the Down-linkis determined in advance and thereby it is possible for the base stationto carry out allocation freely in a range that does not exceed themaximum number of time channels. At this time, instead of determining inadvance the maximum number of time channels that can be allocated to theterminal group that requires transmission power of certain level, it mayalso be possible to cause the base station to have a mechanism foradjusting the maximum number of time channels in accordance with thenumber of adjacent cells by measuring the interference that comes fromthe adjacent cells and estimating the number of adjacent cells.

In addition, a form may also be possible, in which when a plurality oftime channels are allocated to one group, the terminal belonging to thegroup may use any time channel among the plurality of the allocated timechannels and the change of the allocation to a vacant frequency channelof a different time channel is allowed during communication. An exampleof such a case is shown in FIG. 16. As shown in FIG. 16, the terminalsA, C, and D are allocated to the time channel 7 and the terminal F isallocated to the time channel 3, however, these terminals belong to thesame group and therefore it may be allowed to reallocate the terminal Dto the time channel 3 to which the terminal F is allocated. This isbecause the transmission power required for the Down-link to theterminal D and the terminal F is the same level and even if the timechannel to which the terminal D is allocated is changed, the influenceimposed on the adjacent cells does not change.

Similarly, a form may also be possible, in which it is allowed that oneterminal is allocated to another time channel to which another terminalbelonging to the same group is allocated, in addition to the timechannel to which it has been allocated up to now (that is, a pluralityof time channels are allocated to one terminal).

In addition, a form may also be possible, in which when there is avacant frequency channel in the time channel to which the terminal groupthat require high transmission power is allocated, it is allowed thatthe terminal that requires low transmission power is allocated to thevacant frequency channel of the time channel to which the terminal groupthat requires high transmission power is allocated (FIG. 7).

This is because the possibility is high that the terminal group thatrequires low transmission power is allocated to the time channel towhich the terminal group that requires high transmission power isallocated in the adjacent cell, and even if a terminal that requires lowtransmission power is allocated to the vacant frequency channel of thetime channel, no interference between adjacent cells will occur.

On the contrary, however, in a situation in which there exist vacantfrequency channels in the time channel to which a terminal group thatrequires low transmission power is allocated and the number of frequencychannels to be allocated to a terminal that requires high transmissionpower is short, if a terminal that requires high transmission power isallocated to the frequency channel of the time channel to which aterminal group that requires low transmission power is allocated, itfollows that a large interference occurs between adjacent cells. Becauseof this, a form may also be possible, in which instead of allocating aterminal that requires high transmission power to the vacant frequencychannel in the time channel to which a terminal group that requires lowtransmission power is allocated as it is, after the modulation scheme ofthe terminal that requires high transmission power is changed to a lowerone and at the same time, the transmission power is also set to a lowervalue, the allocation to the vacant frequency channel of the timechannel to which the terminal group that requires low transmission poweris allocated is allowed. By employing such a form, even when theallocation to the time channel to which a different terminal group isallocated is carried out, it is possible to suppress interference fromaffecting the adjacent cells by setting transmission power to a lowervalue while avoiding the occurrence of an error caused by the setting ofthe transmission power to the terminal to a lower value.

Next, another form is shown, in which a vacant time channel is reservedfor a terminal that requires high transmission power. As describedabove, in the first embodiment of the present invention, the timechannel of which the interference power measured at the terminal of thegroup is the smallest is allocated among the remaining time channels notallocated in the order from the terminal group that requires the highesttransmission power in the terminal groups having made a request forcommunication. However, when the transmission power required by a grouphaving made a request for communication is not so high, the time channelthe interference power of which is the smallest is allocated to thegroup and after that, even if a request for communication is made at aterminal situated near the cell edge and a group that requires very hightransmission power is formed, it is not possible to allocate the timechannel the interference power of which is the smallest to a new groupthat requires high transmission power.

As a measure for this problem, a form may also be possible, in which atleast one vacant time channel is reserved for a terminal group thatrequires high transmission power. On the contrary, a form may also bepossible, in which at least one vacant time channel is reserved for aterminal group that requires low transmission power. Further, a form mayalso be possible, in which the number of time channels in whichinterference equal to or greater than a certain value is observed(interfered time channels) is counted and the resultant number of timechannels, which is obtained by subtracting the number of interfered timechannels from the total number of time channels, is reserved for aterminal group that requires high transmission power.

As described above, even in a situation in which a terminal thatrequires high (low) transmission power is not in communication, it ismade possible to deal with the case where a terminal makes a request forcommunication in the future by reserving a vacant time channel for aterminal group that requires high (low) transmission power. However,just reserving a vacant time channel is not an effective measure becausethere is the possibility that a terminal group that requires hightransmission power in the adjacent cell is allocated to the reservedtime channel (this hardly leads to a problem when the terminal grouprequires low transmission power).

Consequently, a form may also be possible, in which a time channel for aterminal group that requires high transmission power is reserved bytransmitting dummy data with the same transmission power as that whenthe control information is transmitted in the time channel theinterference power of which has been determined to be the minimum byanother terminal even when there exists no terminal group that requireshigh transmission power. In addition, it may also be possible todetermine in advance a time channel to be reserved to which dummy datais thus transmitted so as to differ from cell to cell.

In a situation in which there exists a terminal that requires hightransmission power and a time channel is allocated, however, the numberof allocated frequency channels is small and most of the frequencychannels of the time channel in question are vacant, a form may also bepossible, in which dummy data is transmitted in a vacant frequencychannel of the time channel in question. Such a form has the advantagethat it is made easier to detect a time channel with high interferencepower at each terminal in the adjacent cells.

Further, as an optional form in which dummy data is transmitted in orderto reserve a time channel for a terminal group that requires hightransmission power, it may also be possible to implement a function ofterminating transmission of dummy data in order to reduce interferenceaffecting the adjacent cells in a situation in which there is not at allany terminal in the cell.

In addition, in a mobile communication system, transmission andreception of control information (base station ID and terminal ID) isperformed generally between a base station and a terminal even for aterminal that has not made a request for communication and the basestation has a grasp as to which terminal exists in the cell of its ownand the terminal has a grasp as to which cell the terminal belongs to.At the base station in a system in which such transmission and receptionof control information is performed between a base station and aterminal, it is possible to estimate how much transmission power isrequired for the Down-link when the data communication with the terminalis started. Consequently, as an optional form in which dummy data istransmitted for the purpose of reserving a time channel, it may also bepossible to implement a function of transmitting dummy data when thereexists a terminal in the cell, which is estimated to require hightransmission power when data communication is started, and ofterminating transmission of dummy data when there exists no terminal inthe cell, which is estimated to require high transmission power whendata communication is started.

As described above, it is possible to reserve a time channel for aterminal that requires high transmission power in the cell of its ownwhile taking into consideration the prevention of interference affectingthe adjacent cells by estimating transmission power required for theDown-link at the base station and performing transmission of dummy databased on the estimation result.

Second Embodiment

A second embodiment is explained below. FIG. 18 is a block diagramshowing the general configuration of a terminal device (mobile stationapparatus). Reference number 181 denotes a reception antenna part, 182denotes a radio reception part, 183 denotes an analog/digital conversionpart (A/D conversion part), 184 denotes a synchronization part forsynchronization of the OFDM symbols, 185 denotes a guard interval (GI)removal part, 186 denotes a serial/parallel (S/P) conversion part, 187denotes an FFT part, 188 denotes a propagation channel estimation anddemapping part, 189-a to 189-1 denotes parallel/serial conversion parts(P/S conversion parts), 190-a to 190-1 denote error correction decodingparts, 191 denotes a demultiplex part, 192 denotes an SINR measurementpart, 193 denotes an RSS measurement part, 194 denotes a control part,and 195 denotes an Up-link transmission part.

The frequency of the radio wave received by the antenna part 181 isconverted into a frequency band in which A/D conversion is possible inthe radio reception part 182. The data converted into a digital signalin the A/D conversion part 183 is synchronized with the OFDM symbols inthe synchronization part 184 and the guard interval is removed in theguard interval removal part 185. After that, the data is paralleled into1,024 data in the S/P conversion part 186. After that, in the FFT part187, the FFT of 1,024 points is performed and the demodulation of thesub-carrier of the 768 waves is performed in the propagation channelestimation and demapping part 188. The necessary data is serialized inthe P/S conversion parts 189-a to 189-1, error correction is performedin the error correction decoding parts 190-a to 190-1, and it is dividedinto the data of each channel in the demultiplex part 191.

The SINR measurement part 192 is a block that measures the SINR for eachsub-channel, which will be described below, using the output of the FFTpart 187, the output of the propagation channel estimation and demappingpart 188, and the output of the error correction decoding parts 190-a to190-1. The RSS measurement part 193 is a block that measures the RSSIfor each sub-channel from the output of the radio reception part 182 andthe output of the FFT part 187. The control part 194 takes out necessaryinformation from the reception data output from the RSS measurement part193, the SINR measurement part 192, and the demultiplex part 191 andsends the Up-link data to the Up-link transmission part 195 inaccordance with the procedure explained below. The Up-link transmissionpart 195 transmits the Up-link data sent from the control part 194 tothe base station.

FIG. 19 is a block diagram showing the general configuration of the basestation (base station apparatus). Reference number 260 denotes ascheduling part, 261 denotes a multiplex part, 262-a to 262-1 denoteerror correction encoding parts, 263-a to 263-1 denote serial/parallelconversion parts (S/P conversion parts), 264 denotes a mapping part, 265denotes a transmission power control part, 266 denotes an IFFT part, 267denotes a parallel/serial (P/S) conversion part, 268 denotes a guardinterval insertion part, 269 denotes a digital/analog conversion part(D/A conversion part), 270 denotes a radio reception part, 271 denotesan antenna, and 272 denotes an Up-link reception part.

Which sub-carrier and which time slot are used to transmit theinformation data is determined in the scheduling part 260 and the datais converted into a data stream in accordance with the result thereof.The converted data is subjected to error correction encoding in theerror correction encoding parts 262-a to 262-1. For example, when thenumber of sub-carriers is 768 waves and the modulation scheme of eachcarrier is the QPSK, the data is converted into the data in 768 lines inunits of two bits. After that, the data corresponding to the amountrequired for the modulation of each carrier is converted in the S/Pconversion parts 263-a to 263-1 and each carrier is subjected tomodulation in the mapping part 264.

After that, by the direction from the scheduling part 260, the amplitudeof each carrier is adjusted in the transmission power control part 265.After that, the IFFT is performed in the IFFT part 266. In the followingexplanation, the number of points of the IFFT is assumed to be 1,024 inorder to generate the OFDM signal of 768 waves. Then, after the data isconverted into serial data in the P/S conversion part 267, a guardinterval is inserted in the guard interval insertion part 268. The guardinterval is inserted in order to reduce interference between symbolswhen the OFDM signal is received.

Then, after converted into the analog signal in the D/A conversion part269, the data is converted into a frequency to be transmitted in theradio reception part 270 and then, the data is transmitted from theantenna part 271. By means of the transmission power control informationand the interference information received by the Up-link reception part272, the scheduling part 260 executes the control properly. The methodof the control is explained below in detail.

The radio wave form used in the second embodiment is the OFDM. It isassumed that the number of sub-carriers used in the Down-link is 768 and64 of sub-carriers are integrated into a sub-channel. Consequently, itfollows that the Down-link consists of 12 sub-channels. This is shown inFIG. 20. In the second embodiment, it is supposed that the number ofsub-channels that can be used is greater than the total number ofadjacent cells.

The MAC has a fixed length frame configuration. In the frame, nine slotsare accommodated. This is shown in FIG. 21. Among these slots, the frontslot of the frame in each sub-channel is a control slot, in whichinformation about the control slot itself and the following slots isstored. The control slots of all of the sub-channels are togetherreferred to as a control slot group.

To the front of each slot, a preamble is added and it is possible forthe reception terminal to perform demodulation of the following datablocks by receiving the preamble and adjusting the demodulation timing.The structure of the slot is shown in FIG. 22( a). The Up-link is notreferred to in particular in the second embodiment. Various techniquescan be utilized. Irrespective whether single carrier or multi carrier,and whether or not a frame configuration is employed, various techniquescan be utilized.

The topology of the network is a star type with the base station as itscenter. The communication data of all of the Down-links are transmitteddirectly from the base station to the terminal. The outline of thetopology is shown in FIG. 22( b).

It is assumed that the cells are arranged in a hexagonal form. The basestation is situated in the center and the base stations are arrangedequidistantly. It is assumed that the total number of adjacent cells issix at the maximum. The outline of the cell arrangement is shown in FIG.23( a). The base station always transmits the control slot to all of thesub-channels.

The following information is stored in the control slot. That is, thenetwork ID, the transmission power information of the control slot ofthe sub-channel, and the terminal ID allocated to each of the followingslots. An example of the structure of the control slot is shown in FIG.23( b).

It is assumed that the control slot is sent by a modulation scheme withhigher reliability than that by which the data slot is sent. This isbecause information of highly great importance is transmitted by thecontrol slot although the amount of information is small. Although themodulation scheme is not specified in particular, in the secondembodiment, it is assumed that the BPSK is used for the control slot andthe QPSK is used for the data slot.

The mobile terminal (mobile station apparatus) demodulates the controlslot transmitted by the base station and makes a request for connectionby sending the terminal ID of its own to the base station of theobtained network ID using the Up-link. When allowing the connection, thebase station having received the request for connection transmits theterminal ID in the slot allocation information in the control slot andorders the terminal to use the slot in the Down-link.

The base station executes transmission power control in order to keepthe transmission power of the radio wave to be transmitted to the mobileterminal to a minimum. Because of this, the mobile terminal receives anddemodulates the control slot group of all of the sub-channels once in atleast n (n: natural number) frames and calculates the propagation lossof the sub-channel from the information of the transmission power ofeach channel shown in each control slot. At the same time, the mobileterminal calculates the SINR of each sub-channel. The mobile terminaltransmits the calculated propagation loss and the SINR of eachsub-channel to the base station via the Up-link.

The base station obtains the propagation loss and the SINR from all ofthe connected mobile terminals via the Up-link. After that, the basestation calculates transmission power required for the transmission ofthe Down-link to each terminal from the propagation loss of eachterminal and classifies the terminals connected to the base station intofour levels (just an example, not limited to four levels). One group isdefined as a group in which data is transmitted from the base stationwith transmission power with which demodulation is possible even at thecell boundary and two groups are defined as a group in which data istransmitted from the base station with transmission power thatsufficiently attenuates at the cell boundary and that does not affectsthe adjacent cells.

The other group is defined as a group in which data is transmitted fromthe base station with transmission power with which demodulation may notbe possible at the cell boundary, however, which may affect the adjacentcells. It is not required for each group to include a terminal as aresult of classification. The relationship between the cell boundary andthe transmission power groups is shown in FIG. 24. In FIG. 24, the areain which demodulation is possible even at the cell boundary is denotedby 2061 and the area that does not affect the adjacent cells is denotedby 2062.

The outline of the operation procedure of the terminal is shown alongwith a flow chart. The flow chart is shown in FIG. 25. First, in stepS2101, the terminal receives the signals of the Down-link and searchesfor a base station that transmits the control slot group. After a basestation that transmits the control slot group is found, the terminaldemodulates the control slot group in step S2102 and analyzes thecontents of the control slot group. In this step, the terminal acquiresthe base station ID of the base station. Next, in step S2103, theterminal transmits the acquired base station ID to the base station viaan Up-link means and makes a request for connection.

After step S2103, in step S2104, the terminal receives the control slotgroup several times and determines whether or not the connection issuccessful depending whether or not the ID of the terminal of its own istransmitted in the control slot. If the connection has failed, theprocedure returns to step S2101 for searching for a base station andwhen it has succeeded, the procedure proceeds to step S2105 formeasurement of the propagation loss and the SINR. In step S2105 formeasurement of the propagation loss and the SINR, the terminal receivesthe Down-link signals from the base station and measures the propagationloss from the base station to the terminal for each sub-channel and theSINR (Signal to Interference and Noise power of Ratio) at the positionof the terminal. Various measurement methods can be thought. Althoughthe detailed description is omitted because they do not related to thecontents of the second embodiment, the methods includes a method inwhich the propagation loss is found from the RSSI (Receive SignalStrength Indicator) of the control slot and the transmission power inthe control slot and the SINR is found from the difference between thereceived waveform of the control slot and the ideal waveform estimatedfrom the demodulated data by demodulating the control slot etc.

In the next step S2106, which is step for transmitting the propagationloss and the SINR, the propagation loss and the SINR found in theprevious step S2105 are transmitted to the base station via the Up-linkmeans.

In the reception process in the next step S2107, the Down-link data forthe terminal of its own is received in accordance with the contents ofthe received control slot. In the next step S2108, the terminaldetermines whether or not the reception of signals from base station ispossible depending on whether the next control slot can be received andwhen reception is possible, the procedure returns to step S2105, whichis step for analyzing the propagation loss and the RSSI and whenreception is not possible, the procedure returns to step S2101, which isstep for searching for a base station. By repeating these steps, thecommunication of the Down-link can be maintained.

Next, the outline of the operation procedure of the base station isshown along with a flow chart. First, in step S2001, the base stationperforms a process to allocate a sub-channel that can be used to eachtransmission power group. Next, in step S2002, the base station checkswhether or not there exists a terminal that has newly made a request forconnection and performs the connection process in step S2003 when thereexists any. Irrespective of the execution in step S2003, the basestation performs the transmission power control in step S2004. Then, thebase station performs the determination of a transmission sub-channel instep S2005 and the procedure returns to step S2001 when the result is NGand the base station allocates a sub-channel that can be used. When theresult is OK, the procedure proceeds to step S2007 for the allocation oftransmission data slot.

After the step for the allocation of transmission data slot, the basestation performs Down-link transmission in accordance with theallocation in step S2008 and the procedure returns to step S2002 inwhich whether or not there exists a terminal that has newly made arequest for connection is checked.

At the time of the transmission of the Down-link, the transmission powerfor each sub-channel is controlled in accordance with the transmissionpower of the transmission power group allocated to the sub-channel. Thecontrol slot is also transmitted in accordance with this control bydisplaying the transmission power in the transmission power informationin the control slot. However, although explanation will be given later,there may be the case where the data of a terminal of anothertransmission power group is allocated to the data slot part. In thiscase, only the slot shall be transmitted with the transmission powerdefined by the transmission power group.

Next, the detail part of the operation procedure of the base station isexplained along with a flow chart. The contents of the process of thestep for the allocation of sub-channel that can be used are explained.The flow chart is shown in FIG. 27. First, in step S2201, the mostrecent propagation losses sent from all of the terminals via the Up-linkmeans are totalized. In the next step S2202, the transmission power foreach terminal is classified into four levels according to the totalizedpropagation loss and all of the terminals are classified into groups oftransmission power. In the next step S2203, the most recent SINR foreach sub-channel sent from all of the terminals via the Up-link means istotalized. In the next step S2204, the minimum value of the SINR isfound for each sub-channel. In the next and subsequent steps, theallocation of sub-channel that can be used is carried out actually foreach transmission power group.

In the second embodiment, it is assumed that one, four, four, and threesub-channels are allocated to each group in the descending order of thetransmission power. Only one sub-channel is allocated to the group withthe strongest transmission power, and this is because the value of thenumber of the total number of sub-channels/(total number of adjacentcells+1) is prevented from being exceeded.

In step S2205, first, the group with the largest transmission power isfocused on and allocation is carried out for the group focused on instep S2206. The predetermined number of sub-channels is allocated in theorder from the sub-channels with the largest minimum SINR among thesub-channels, that is, in the order from the sub-channels with thesmallest interference. In step S2207, whether or not there remains agroup to which a sub-channel that can be used has not been allocated yetis checked and if there remains any, a group with the second strongesttransmission power is focused on in step S2208 and step S2206, which isstep for the allocation of sub-channel, is repeated and when thereremains no group to which the sub-channel that can be used has not beenallocated yet, the allocation of sub-channel that can be used isterminated.

Next, the detailed procedure of the step of connection process isexplained. A flow chart is shown in FIG. 28. First, in step S2301, theterminal ID sent by a terminal via the Up-link means is registered asone that can be used at the base station. At this time, only once, theslot for the terminal is allocated for the sub-channel allocated to thegroup with the maximum transmission power. Due to this, the terminalknows that the request for connection has been accepted. In addition,during the allocation of the slot, the slot may be embedded with dummydata. In the next step S2302, the base station waits until the terminalsends the propagation loss and the procedure proceeds to the next step.In the next step S2304, to which transmission power group this terminalshould belong is calculated from the sent propagation loss. In the nextstep S2304, this terminal is added to the group, as a result of thecalculation, and the step of connection process is terminated.

Next, the detailed procedure of the transmission power control step isexplained. A flow chart is shown in FIG. 29. First, in step S2401, themost recent propagation losses sent from all of the terminals aretotalized. In the next step S2402, the transmission power to eachterminal is set to a four-level transmission power based on thepropagation loss obtained in the previous step and in the next stepS2403, grouping is performed according to the set transmission power.Then, the transmission power control step is terminated.

Next, the detailed procedure of the determination of the allocation ofsub-channel is explained. A flow chart is shown in FIG. 30. First, instep S2501, the most recent SINR for each sub-channel sent from all ofthe terminals is totalized. In the next step S2502, whether or not theSINR of the sub-channel allocated to the terminal satisfies apredetermined value is checked for each terminal. Determination is madein step S2503 and when the SINR satisfies the predetermined value at allof the terminals, OK is issued as the result of determination in stepS2504 and when any one of the SINRs does not satisfy the predeterminedvalue, NG is issued as the result of determination in step S2505, andthen the step of the determination of the allocation of sub-channel isterminated.

Next, the detailed procedure of the allocation of transmission data slotis explained. A flow chart is shown in FIG. 31 and FIG. 32. First, instep S2601, the group with the largest transmission power is focused on.In the next step S2602, the total amount of data to be transmitted tothe terminals included in the focused-on group is checked and how manyslots are required for the data is calculated. In step S2603, when thereis not data to be transmitted and the number of necessary slots is zero,the procedure proceeds to the determination as to whether or not thereis an unevaluated transmission power group in step S2613 and when thenumber of necessary slots is one or more, the procedure proceeds to thecalculation of the number of unused slots in step S2604. In step S2604of the calculation of the number of unused slots, the total number ofvacant slots of the focused-on group and the group to which transmissionpower larger than that of the focused-on group is allocated iscalculated.

In the next step S2605, the number of slots required for transmission iscompared with the calculated number of vacant slots and whether or notthe number of vacant slots is sufficient is determined. When sufficient,all of the data for which a request for transmission has been made astransmission data is regarded as transmission data in step S2606, andwhen the number of vacant slots is not sufficient, data corresponding tothe number of vacant slots is cut out from the data for which a requestfor transmission has been made and regarded as transmission data in stepS2607. At this time, in order to prevent only the data bound for aspecific terminal from being cut out, the data is cut out by the roundrobin method for all of the terminals in the group. Due to this, thethroughput of a specific terminal is prevented from reducing.

In the next step S2608, the prepared transmission data is divided foreach terminal. In the next step S2609, the priority of the terminals isdetermined. The initial value of the process method of the priorityshall be the order of the terminal ID and the terminal processed oncewith the highest priority will be processed with the lowest prioritynext time, that is, the round robin method shall be used.

By performing this process, it is avoided that only a specific terminalis processed. In the next step S2610, data is allocated to the vacantslots of the sub-channel allocated to the focused-on group in the orderof the priority set to the terminals. At this time, when there are twoor more sub-channels that can be used, allocation is carried out in theorder from the sub-channel with the lowest SINR. When there remainstransmission data that is not allocated after the data is allocated toall of the vacant slots of the sub-channel allocated in step S2611, thedata is allocated also to the vacant slots of the sub-channel allocatedto a group with transmission power larger than that of the focused-ongroup until all of the transmission data is allocated in step S2612.

In the next step S2613, whether or not there remains a group withtransmission power smaller than that of the transmission power groupcurrently focused on is checked, that is, whether or not there remainsan unprocessed group is checked, and when there remains any, a groupwith transmission power second in magnitude to that of the groupcurrently focused on is focused on in step S2614 and then the procedurereturns to step S2602 in which the number of slots for the data to betransmitted to the terminals in the group is calculated, and when thereremains none, the step of the allocation of transmission data slot isterminated.

Next, how interference between cells is avoided when there exist thebase station and the terminal group that operate as described above isexplained. First, a situation is supposed, in which the allocation ofthe same sub-channel that can be used is carried out by coincidence inadjacent cells. This situation is shown in FIG. 33. Although this is aspecial situation, it can occur depending on the position of theterminals in the cells, such as when the terminals in one of the cellsare arranged only in the vicinity of the base station etc. Here, a caseis considered, where one of the terminals in the vicinity of the basestation moves near to the cell boundary. This case is shown in FIG. 34.Here, a terminal b moves near to the position at which both the cellsneighbor each other. Since the adjacent cell also arranges the samesub-channel, the SINR of a sub-channel (1) to be allocated newly to theterminal that has moved will deteriorate. The terminal having moveddemodulates the control slot and reports the SINR and the propagationloss of all of the sub-channels at the position to which it has moved tothe base station via the Up-link.

The base station learns that the classification of the transmissionpower groups is correct no longer by the fact that the propagation losssent by the terminal that has moved becomes large. The base stationnewly reconfigures the transmission power groups and determines, byreferring to the SINR sent from the terminals to be added newly to therespective transmission power groups, whether or not the sub-channelthat can be used allocated to the transmission power group to which theterminal is newly added can be used without problem.

In this example, since the allocated sub-channel (1) is affected by theadjacent cell, the SINR is below that which can be used and it isdetermined that the sub-channel cannot be used. In response to this, inthe cell A, the reallocation of sub-channel that can be use is carriedout. At this time, evaluation is made in the order from the group withthe largest transmission power. Since the allocation is carried outbased on the SINR evaluated by the terminal b belonging to the group,the sub-channel is selected from among (10, 11, 12) with excellent SINR.Here, (12) is selected. After that, sub-channels with excellent SINR areselected in the descending order of the transmission power of the groupand as a result, a sub-channel with poor SINR is allocated to the groupwith the smallest transmission power. The situation after the allocationis shown in FIG. 35.

Here, the distance of the terminal in the group with small transmissionpower from the other cell is sufficiently large and in actuality,communication is possible without problem although the evaluation of theSINR is poor more or less. In addition, the transmission power is alsosmall and therefore the signals of the sub-channel used in this grouphardly affects the other cell. As a result, wireless interference doesnot occur between the two cells and therefore the communication betweenthe base station and the terminals is enabled.

The operation is the same also when there are a plurality of cells.Since up to one (total number of sub-channels that can be used/(numberof adjacent cells+1)) sub-channel that can be used is allocated to thegroup with transmission power that can reach the adjacent cell, even ifmost of sub-channels are affected by all of the adjacent cells, it isunlikely that the system fails because it is no longer possible toallocate transmission power that can reach the adjacent cell in thecell.

Similarly, the adjacent cell is in a state in which it is possible toprepare one or more sub-channels ((total number of sub-channels-numberof adjacent cells−1).gtoreq.1) that does not affect the cell boundary,and therefore, it is made possible to attain a sub-channel arrangementwithout interference in the cell even when affected by all of theadjacent cells.

Even when the result of rearrangement is inconvenient to other cells, ifrearrangement of sub-channels is carried out each time, the ratio of thenumber of sub-channels that can reach the adjacent cells is set equal toor less than a certain value, and therefore, the sub-channels that reachthe adjacent cells become dispersed gradually in the entire cell and theoperation without interference is enabled in the entire system.

Next, the operation when a cell is added newly is explained. First, asituation is supposed, in which three cells (cell A, cell B, cell C) arearranged and arrangement of sub-channels has already been carried outproperly between the cells. This state is shown in FIG. 36. Next, asituation is supposed, in which a cell D is arranged in such a manner asto be adjacent to the cell B and cell C. This state is shown in FIG. 37.Here, a situation is supposed, in which the cell C and the cell D havecarried out the same sub-channel arrangement due to the influence of thearrangement of terminals after the arrangement. As shown in FIG. 37, itcan be thought that such a situation occurs when the arrangement stateof terminals in the cell D is a state in which a terminal, such as aterminal f, is not affected by the cell C and only the influence fromthe cell B can be detected.

In this state, when a terminal e in the cell C moves near to theboundary with the cell D, interference from the cell D is detectednaturally. This state is shown in FIG. 38. In this case, by performingthe process in accordance with the above-described procedure, theallocation of the sub-channels in the cell C is changed. At this time,when a terminal is arranged between the cell A and the cell B, theinfluence from the adjacent cells is detected and arrangement ofsub-channels is carried out in the cell such that there is nointerference among all of the cells. Since the sub-channel that affectsthe adjacent cells is avoided with priority, allocation is carried outas long as possible. An example of the final allocation is shown in FIG.39.

Third Embodiment

In the above explanation, an embodiment in which the maximum value ofthe number of adjacent cells is determined in advance is explained. Bychanging part of the procedure described above, it is made possible todeal with a case where the maximum number of adjacent cells changesdynamically. If the maximum number of adjacent cells is determined inadvance, the number of sub-channels allocated to a group that performstransmission with transmission power that reaches the cell edge islimited. In the above-described example, since the six cells neighboreach another, only one sub-channel can be allocated to this group. Dueto this, in the case where terminals have gathered together near thecell edge, a problem arises in that the usage efficiency of thesub-channels in the cell decreases.

For this problem, it is made possible to improve the efficiency byallocating more sub-channels to a group with transmission power that canreach the cell edge in the case where the number of adjacent cells issmaller or in the case of isolated cell. A third embodiment is explainedbelow.

In the third embodiment, a means for checking the number of currentadjacent cells is added to the base station in addition to the case ofthe above-described second embodiment. The means for checking the numberof adjacent cells may use any method. For example, such a methodsuggests itself, in which a high-gain antenna is added in addition tothe antenna the gain of which has adapted to the cell radius normallyused by the Up-link, and thereby the Up-link communication of a terminalsituated beyond the cell radius is received, and the number of adjacentcells is checked by checking which base station ID is used.

By the way, the operation of the terminal may be quite the same as thatin the second embodiment described above. The operation of the basestation is also the same basically. However, part of the contents of thestep of the allocation of sub-carrier that can be used (FIG. 26, S2001)is changed. In the above-described second embodiment, the number ofsub-channels allocated in step S2001 for the allocation of sub-channelthat can be used is set fixedly to one, four, four, and three in thedescending order of transmission power. This step is changed as follows.A flow chart is shown in FIG. 40.

In the first step S2701, the number of adjacent cells is checked. In thenext step S2702, the number of sub-channels allocated to a group withtransmission power that reaches the cell edge is calculated. This numberis assumed to be (total number of sub-channels/(number of currentadjacent cells+1)) (decimal fraction is rounded down). In the next stepS2703, a group with transmission power that reaches the cell edge isfocused on. In the next step S2704, a sub-channel is allocated to thefocused-on group with transmission power that reaches the cell edge. Atthis time, the most recent minimum SINR for each sub-channel collectedby the base station is checked and allocation is carried out in thedescending order of the minimum SINR. In the next step S2705, whether ornot there is a transmission power group to which a sub-channel has notbeen allocated yet is determined and when there is any unallocatedgroup, the procedure proceeds to step S2706 and when there is nounallocated group, the step of the allocation of sub-channel that can beused is terminated. In step S2706, a group with transmission powersecond in magnitude to that of the transmission power group currentlyfocused on is focused on. In the next step S2707, the number ofsub-channels allocated to the focused-on group is calculated.

Here, it is assumed that when the number of groups to which asub-channel is not allocated is one, that is, when the unallocated groupis only the group currently focused on, the number shall be the totalnumber of remaining sub-channels, and when the number of groups to whicha sub-channel has not been allocated yet is more than one, the numbershall be ((number of unallocated sub-channels)/(number of groups towhich the number of sub-channels is not allocated) (decimal fraction isrounded up). In the next step S2708, the number of sub-channelscalculated in step S2707 is allocated to the focused-on group. Afterthat, the procedure returns to step S2705, in which evaluation of theremaining groups is continued.

By dynamically changing the number of sub-channels to be allocateddepending on the number of adjacent cells in this manner, it is possibleto avoid a situation in which the number of sub-channels to be allocatedto a specific group becomes less than required.

Fourth Embodiment

In the above-mentioned embodiment, it is premised that there is alwaysinterference from the adjacent cell. However, it is possible to increasethe number of sub-channels with transmission power that reaches theadjacent cells by evaluating only the sub-channels actually affected bythe adjacent cells. An embodiment in this case is shown below.

In a fourth embodiment, the operation of the terminal may also be quitethe same as that in the above-described second embodiment. The operationof the base station is also the same basically. However, part of thecontents of the step of the allocation of sub-channel that can be used(FIG. 26, S2001) is changed as in the third embodiment describedimmediately above. A flow chart is shown in FIG. 41.

In the first step S2801, the number of interfered sub-channels ischecked. A means for checking the number of interfered sub-channels isnot specified in particular. For example, a method suggests itself, inwhich the SINR of each sub-channel obtained from all of the terminals ischecked and a sub-channel in which the SINR is below a predeterminedvalue at any one of terminals is handled as an interfered sub-channel.In the next step S2802, the number of sub-channels to be allocated to agroup with transmission power that reaches the cell edge is calculated.It is assumed that this number is (total number of sub-channels that canbe used-currently interfered sub-channels), however, when this numberexceeds half the total number of sub-channels that can be used (here,half is used, however, not limited to half), this number is half thetotal number of sub-channels that can be used. This is in order to copewith a case where the number of interfered sub-channels is calculated asa number less than the correct number and to leave the margin toallocate a sub-channel to a group that does not affect the adjacentcells in the cell of its own. In the next step S2803, a group withtransmission power that reaches the cell edge is focused on. In the nextstep S2804, a sub-channel is allocated to the focused-on group withtransmission power that reaches the cell edge.

At this time, the most recent minimum SINR for each sub-channelcollected by the base station is checked and allocation is carried outin the descending order of the minimum SINR. In the next step S2805,whether or not there is a transmission power group to which asub-channel has not been allocated yet is determined and when there isan unallocated group, the procedure proceeds to S2806 and when there isno unallocated group, the step of the allocation of sub-channel that canbe used is terminated. In step S2806, a group with transmission powersecond in magnitude to that of the transmission power currently focusedon is focused on. In the next S2807 step, the number of sub-channels tobe allocated to the focused-on group is calculated. Here, it is assumedthat when the number of groups to which a sub-channel is not allocatedis one, that is, when the unallocated group is only the group currentlyfocused on, the number is the total number of remaining sub-channels,and when the number of groups to which a sub-channel has not beenallocated yet is more than one, the number is ((number of unallocatedsub-channels)/(number of groups to which the number of sub-channels isnot allocated))(decimal fraction is rounded up). In the next step S2808,the number of sub-channels calculated in step S2807 is allocated to thefocused-on group. After that, the procedure returns to step S2805, inwhich evaluation of the remaining groups is continued.

By thus controlling and by increasing or decreasing the number ofsub-channels to be allocated to the group with transmission power thatreaches the adjacent cells depending on the magnitude of theinterference from the adjacent cells, it is made possible to allocatemore sub-channels to the group with transmission power that reaches theadjacent cells. In this case, even when many sub-channels are allocatedto the group with transmission power that reaches the adjacent cells, ifthe amount of communication of this group is small, it is also possibleto allocate communication of a group with smaller transmission power,and therefore, communication is performed almost without a decrease inthe efficiency in the cell.

In the above embodiments, control is performed in units of sub-channels,a collection of sub-carriers, however, control can be performedsimilarly in units of sub-carriers.

Fifth Embodiment

Next, a grouping method of terminals by a control station (base station)when the quality of targeted communication differs from group to groupin a grouping method of terminals by the control station according todistances from the terminals and the control station etc. is explained.This corresponds to a system in which communication of high speed isperformed with a terminal that is near the control station, that is, aterminal the reception SNR of which can be thought to be high, and onthe other hand, communication of low speed is performed with a terminalthat is at the cell edge, that is a terminal the reception SNR (or SINR)of which can be thought to be low.

When an adaptive modulation is used in the above-mentioned system, thereis a problem in that the communication speed of a terminal having asubtle value with respect to the reference of grouping is not constantor the communication speed needs to be changed frequently.

In a fifth embodiment, therefore, a method for giving the nature ofhysteresis to grouping is explained. Using FIG. 48, the grouping methodis explained by an example. The horizontal axis in FIG. 48 representsthe transmission power level supposed to be required by the respectiveterminals for reception (referred to a supposed reception power) and thevertical axis represents the destination of grouping according to theindividual supposed reception power. In the fifth embodiment, it followsthat all of the terminals are grouped into four groups. The solid linein FIG. 48 indicates the reference value of grouping in the case ofmovement in the increasing direction of the supposed reception power (inthe rightward direction in the graph) and the dotted line indicates thereference value of grouping in the case of movement in the decreasingdirection thereof (in the leftward direction in the graph).

Here, for example, when the supposed reception power of a terminalchanges A to B, it follows that the terminal moves from group B to groupC when the supposed reception power is TC and when the supposedreception power of a terminal from B to A, it follows that the terminalmoves from group C to group B moves when the supposed reception power isTD. By performing such control, it is possible to solve a problem inthat the communication speed is not constant and a problem in that thecommunication speed needs to be changed frequently.

In addition, there may be a case where regrouping of connected terminalsis performed when a cell is made to a new terminal etc. At this time, byperforming grouping of terminals having supposed reception power in thehysteresis loop (In FIG. 48, for example, where the supposed receptionpower is between TD and TC) last, it is made possible to performefficient regrouping even in the case of crowded terminals. When therearises a need of regrouping, the base station groups terminals inaccordance with the dotted line in FIG. 48. Following the dotted lineresults in grouping that attains a transmission rate as high aspossible. If there remains unevenness in grouping after it is performedin accordance with the dotted line, it is made possible to reduce theunevenness by exchanging the terminals having the supposed receptionpower on the dotted line. This utilizes the fact that communication ispossible even when the terminals in the hysteresis loop belong towhichever group. By the way, after once grouped, movement is madebetween groups as shown at the beginning of the fifth embodiment.

As described above, according to the fifth embodiment, it is also madepossible to efficiently perform regrouping by setting the hysteresisloop.

Sixth Embodiment

The grouping in the first to fifth embodiments premise that thetransmission power of the base station is controlled so that thereception power is approximately constant irrespective of the distancefrom the base station to the terminal.

However, when the transmission power control of the base station asdescribed above is performed, it follows that the largest transmissionpower is allocated to the terminal near the cell boundary. If it isassumed that the terminals are distributed uniformly in the cell, theratio of the terminals near the cell boundary is large and thereforelarge transmission power is allocated to many terminals and theinterference power affecting the adjacent cells increases as a result.

In the present embodiment, it is not required necessarily for thereception power at the terminal to be constant. In a sixth embodiment, acase is shown, where a plurality of values are used as reception powerat a terminal at the time of grouping according to the propagation loss.

FIG. 49 shows an example of the grouping condition. In this example, thewhole is divided into five groups using the propagation loss includingthe influence of the variation in the propagation channel, such asfading, and three kinds of reception target SNR are set for therespective groups. A control flow of a base station is shown in FIG. 50and a control flow of a terminal is shown in FIG. 51 when grouping isperformed in the above-described manner.

First, the control flow of a base station is explained in detail. By theway, the same frame format is used as that in FIG. 21.

First, in step S501, a signal for measuring SNR and information oftransmission power of the current control slot are transmitted using thecontrol slot. Any signal for measuring SNR may be used. For example, aknown signal may be used, in which part of the OFDM sub-carrier is nullcarrier. In this case, it is possible to find the SNR by comparing thestrength of the transmitted carrier and the null carrier on thereception side. Next, in step S502, the propagation loss and informationof SNR of the control signal are acquired from each terminal via theUp-link. Next, in step S503, the respective terminals are groupedaccording to the propagation loss notified from each terminal. At thistime, it is assumed that the grouping in FIG. 49 is obeyed.

Next, in step S504, transmission power to be allocated to each of thegrouped terminals is determined. It is assumed that the transmissionpower is a value determined in advance based on the worst SNR in itsgroup. After that, in step S505, Down-link data is transmitted to eachterminal using the slot for which allocation has been determined in theprevious frame. After that, in step S506, the allocation of the slot tobe used in the next frame is determined as well as that of thetransmission power found in step S504 and the setting is so made thatthe contents are transmitted using the next control slot. When theadaptive modulation is performed, it is possible to set a modulationparameter by referring to the SNR information obtained from the terminalwhen the allocation is determined.

After that, the flow returns to step S501, where the above procedurefrom the transmission of the control slot is repeated.

Next, the control flow of a terminal is explained in detail. First, instep S511, the control slot transmitted from the base station isreceived. Next, in step S512, the propagation loss from the base stationto the terminal and the SNR of the received control slot are measured.Any method for finding the propagation loss and SNR may be used. Forexample, it is possible to use a value as the propagation loss, which isthe transmission power of the control slot at the base station includedin the control slot minus RSSI. To be precise, this value is not thepropagation loss, however, since the relative value between terminalscan be known if the same measurement is performed at all of theterminals, it is possible to use this value as the propagation loss. Inaddition, it is possible to measure the SNR by transmitting a knownsignal in which part of sub-carrier is null carrier to the base stationand by finding the transmission power ratio between a certain carrierand the null carrier of the signal.

Next, the information of the propagation loss and SNR measured in stepS513 is transmitted to the base station via the Up-link. After that, instep S514, the data is received based on the allocated informationincluded in the control slot. After that, the flow returns to step S511and the procedure from the reception of the control slot is repeated.

Due to the above operation of the base station and the terminal, theallocation of slot in accordance with the parameters determined as shownin FIG. 49 and the transmission power control are performed. By the way,the allocation of slot may be carried out in the direction of timechannel or in the direction of frequency channel and it is possible tocarry out by combining each of the above-mentioned embodiments.

Seventh Embodiment

In the first to sixth embodiments, a configuration based on the OFDM isemployed. However, the present invention can be applied to other thanthe OFDM. For example, in the case of SS (Spread Spectrum), it is notpossible to perform group control by the frequency channel, however,group control can be performed by the time channel and it is madepossible to perform the present invention.

INDUSTRIAL APPLICABILITY Explanations of Letters or Numerals

-   -   100 antenna part    -   101 radio reception part    -   102 A/D conversion part    -   103 synchronization part    -   104 guard interval removal part    -   105 S/P conversion part    -   106 FFT part [0284]    -   107 propagation channel estimation and demapping part    -   108-a to 108-1 P/S conversion part    -   109-a to 109-1 error correction decoding part    -   110 demultiplex part    -   111 A/D conversion part    -   112 RSS measurement part    -   113 interference power measurement part    -   114 control part    -   115 Up-link transmission part    -   120 scheduling part    -   121 multiplex part    -   122-a to 122-1 error correction encoding part    -   123-a to 123-1 S/P conversion part    -   124 mapping part    -   125 transmission power control part    -   126 IFFT part    -   127 P/S conversion part    -   128 guard interval insertion part    -   129 D/A conversion part    -   130 radio transmission part    -   131 antenna part    -   181 antenna part    -   182 radio reception part    -   183 A/D conversion part    -   184 synchronization part    -   185 guard interval removal part    -   186 S/P conversion part    -   187 FFT part    -   188 propagation channel estimation and demapping part    -   189-a to 189-1 P/S conversion part    -   190-a to 190-1 error correction decoding part    -   191 demultiplex part    -   192 SINR measurement part    -   193 RSS measurement part    -   194 control part    -   195 Up-link transmission part    -   260 scheduling part    -   261 multiplex part    -   262-a to 262-1 error correction encoding part    -   263-a to 263-1 S/P conversion part    -   264 mapping part    -   265 transmission power control part    -   267 IFFT part    -   267 P/S conversion part    -   268 guard interval insertion part    -   269 D/A conversion part    -   270 radio transmission part    -   271 antenna part    -   272 Up-link reception part

What is claimed is:
 1. A base station apparatus used in a wirelesscommunication system, said base station apparatus comprising: acommunication unit which communicates with a mobile station apparatusutilizing communication resources configured by arranging a plurality offirst regions defined by frequency and times axes; an acquiring unitwhich, in response to communicating with the mobile station apparatus,acquires at least one different indicator for each second region whichis configured by arranging the first regions in the frequency directionor in the time direction prior to performing scheduling of one or moreof the first regions to be used in the communication from thecommunication resources, wherein the indicator is information which isconcerned with at least a level of transmission power to be used in thesecond region by a second base station other than said base station. 2.The base station apparatus according to claim 1, wherein saidinformation which is concerned with at least a level of transmissionpower to be used in the second region by said second base station isinformation which indicates interference power that arrives at insidethe cell controlled by said base station apparatus from said second basestation.
 3. The base station apparatus according to claim 2, furthercomprising: a controller which controls transmission power of each timechannel or frequency channel in transmitting a radio signal to a mobilestation apparatus located in the cell controlled by said base stationapparatus, based on said information which indicates interference powerthat arrives from said second base station.
 4. The base stationapparatus according to claim 3, wherein said information which indicatesinterference power is notified from at least one mobile stationapparatus located in the cell controlled by said base station apparatus.5. The base station apparatus according to claim 3, wherein a timechannel or frequency channel considered using lower transmission powerthan a predetermined threshold value in transmitting a downlink radiosignal in said second base station is controlled to transmit a downlinkradio signal to mobile station apparatuses located in the cellcontrolled by said base station apparatus using higher transmissionpower than said transmission power in said second base station.
 6. Thebase station apparatus according to claim 3, wherein a time channel orfrequency channel considered using higher transmission power than apredetermined threshold value in said second base station intransmitting a downlink radio signal is controlled to transmit adownlink radio signal to mobile station apparatuses located in the cellcontrolled by said base station apparatus using lower transmission powerthan said transmission power in said second base station.
 7. The basestation apparatus according to claim 6, wherein said lower transmissionpower is minimum transmission power to said base station apparatus. 8.The base station apparatus according to claim 3, wherein transmissionpower values required for downlink transmission to said mobile stationapparatuses are calculated for each of said mobile station apparatusesbased on at least propagation loss of each of said mobile stationapparatuses, said calculated transmission power values, which arerequired for downlink transmission to said mobile station apparatuseslocated in the cell controlled by said base station apparatus, aredivided into a plurality of ranges by predetermined threshold, aplurality of said mobile station apparatuses whose calculatedtransmission power values are included in an identical range of saidplurality of ranges is grouped, and each of transmission signals to betransmitted respectively to said mobile station apparatuses belonging tosaid identical group is allocated to a slot of a same time channel orsame frequency channel whose transmission power is the nearest to thetransmission power of said identical group by comparing a level of thetransmission power of each time channel or each frequency channelcontrolled based on the information which indicates interference powerwith a level of the transmission power of mobile station apparatusesconstituting the group.
 9. The base station apparatus according to claim8, wherein the transmission power value required for downlinktransmission to each of said mobile station apparatuses is calculatedbased on propagation loss of each of said mobile station apparatuses sothat reception power in each mobile station apparatus is substantiallyconstant.
 10. The base station apparatus according to claim 3, whereinsaid transmission power of each of time channels or each of frequencychannels is updated at fixed time intervals.
 11. The base stationapparatus according to claim 3, wherein said transmission power of eachof time channels or each of frequency channels is updated when saidinformation which indicates interference power that arrives from saidsecond base station is updated.
 12. The base station apparatus accordingto claim 3, wherein when said transmission power of each of timechannels or each of frequency channels is updated, transmission power iscontrolled so that a difference between transmission power immediatelybefore update and transmission power to be allocated at the time ofupdate is equal to or less than a predetermined value.
 13. The basestation apparatus according to claim 3, wherein at least one or moretime channels or frequency channels are set and controlled so that saidbase station apparatus performs transmission using maximum transmissionpower to said base station apparatus.
 14. The base station apparatusaccording to claim 13, wherein control signals are transmitted on a partof said time channels or frequency channels controlled so that said basestation apparatus performs transmission using the maximum transmissionpower to said base station apparatus.
 15. The base station apparatusaccording to claim 14, wherein said part of time channels or frequencychannels to transmit control signals are changed based on saidinformation which indicates interference power that arrives from saidsecond base station.
 16. The base station apparatus according to claim13, wherein dummy data is transmitted on at least one time channel orfrequency channel controlled so that said base station apparatusperforms transmission using the maximum transmission power to said basestation apparatus.
 17. The base station apparatus according to claim 8,wherein said grouping of a plurality of said mobile station apparatusesis done again when there exists a mobile station apparatus that newlymakes a request for connection in the cell or when any one of mobilestation apparatuses moves and propagation loss changes in a mobilestation apparatus located in the cell.
 18. The base station apparatusaccording to claim 8, wherein said grouping of a plurality of saidmobile station apparatuses is done again at fixed time intervals. 19.The base station apparatus according to claim 8, wherein hysteresischaracteristics are given to conditions to change a group in which amobile station apparatus is included when said grouping is done again.20. A wireless communication system in which a base station apparatuscommunicates with a mobile station apparatus utilizing communicationresources configured by arranging a plurality of first regions definedby frequency and times axes, the wireless communication systemcomprising: the mobile station apparatus; the base station apparatuswhich, in response to communicating with the mobile station apparatus,acquires at least one different indicator for each second region whichis configured by arranging the first regions in the frequency directionor in the time direction prior to performing scheduling of one or moreof the first regions to be used in the communication from thecommunication resources, wherein the indicator is information which isconcerned with at least a level of transmission power to be used in thesecond region by a second base station other than said base station.